JP4315291B2

JP4315291B2 - Seismic isolation ground formation method

Info

Publication number: JP4315291B2
Application number: JP2005086499A
Authority: JP
Inventors: 淳紀沼田; 雅行筒井; 剛治國生; 研而石原
Original assignee: Tobishima Corp
Current assignee: Tobishima Corp
Priority date: 2005-03-24
Filing date: 2005-03-24
Publication date: 2009-08-19
Anticipated expiration: 2025-03-24
Also published as: JP2006265962A

Description

本発明は、軟弱地盤を改良地盤に、さらには改良地盤の下層に免震層を形成する免震地盤形成方法にかかり、特に地表面近くの軟弱地盤について、いわゆる過圧密履歴（一度大きな荷重を受け、再び元の荷重に戻ること）を利用することによって自動的に非軟弱地盤への地盤改良が行え、しかも前記改良した非軟弱地盤の下層に存する軟弱地盤を所定範囲残置することにより、前記軟弱地盤層を免震地盤として機能させる免震地盤形成方法に関するものである。 The present invention relates to a seismic isolation ground forming method in which soft ground is formed into improved ground, and further, a seismic isolation layer is formed in the lower layer of the improved ground. Receiving and returning to the original load again) can automatically improve the ground to the non-soft ground, and by leaving the predetermined range of the soft ground existing in the lower layer of the improved non-soft ground, The present invention relates to a method for forming a base-isolated ground that allows a soft ground layer to function as a base-isolated ground .

一般には、「地盤が液状化することは危険なこと」といった認識が未だ存する。 In general, there is still a recognition that it is dangerous for the ground to liquefy.

このような認識が底辺に未だあるため、レベル１地震動（所定期間内に１〜２度発生する確率を持つ地震動強さ）の揺れで液状化する地盤も、レベル２地震動（発生確率は低いが、断層近傍で発生するようなきわめて激しい地震動強さ：マグニチュード６．５程度の直下型地震による地震動を下限とする）の揺れで液状化する地盤も同様に捉えてしまう傾向がある。 Since this recognition is still at the bottom, the ground that liquefies due to the shaking of Level 1 ground motion (the strength of ground motion having the probability of occurring once or twice within a predetermined period) is also Level 2 ground motion (the probability of occurrence is low). The ground that liquefies due to the tremendous intensity of strong ground motion that occurs near the fault (with the lower limit being the ground motion due to a direct earthquake with a magnitude of about 6.5) tends to be captured in the same way.

また、構造物全体系での損傷とは別に地盤の液状化だけを捉え、液状化が生じる地盤は必ず液状化対策を講じなければならない、すなわち、とにかく液状化の発生を抑えなければならないといった発想に至っていることが多々ある。 In addition, the idea that the ground where liquefaction should be taken must be taken without regard to the liquefaction of the ground separately from the damage of the whole structure system, that is, the liquefaction should be suppressed anyway. There are many things that have led to.

しかして、その後、前記のような発想は徐々に変化するに至った。 After that, the above-mentioned idea gradually changed.

構造物全体系での耐震性能を考えた場合、地盤の液状化が生じるかどうかということよりも、液状化した地盤で構造物がどのような耐震性能を有しているのかという問題の方がより重要であると考えられるに至ったのである。 When considering the seismic performance of the entire structure system, the question of what seismic performance the structure has on the liquefied ground is better than whether the ground liquefies or not. It came to be considered more important.

そこで、このような基礎データを得るために，過去の地震について、地盤の液状化程度，地震動の大きさ，構造物被害，人的被害の状況などの調査が実施されるに至った。 Therefore, in order to obtain such basic data, surveys were conducted on past earthquakes, such as the degree of ground liquefaction, magnitude of ground motion, structural damage, and human damage.

ここで、これらの地震動に対する土木構造物の保有すべき耐震性能としては、例えば、以下のように設定できる。
（１）レベル１地震動に対しては、原則として構造物の機能が維持されていなければならない。
（２）レベル２地震動に対しては、構造物の重要度を考慮して、これら構造物の保有すべき耐震性を考慮しなければならない。 Here, as an earthquake-resistant performance which the civil engineering structure should have for these earthquake motions, for example, it can be set as follows.
(1) In principle, the function of the structure must be maintained for Level 1 ground motion.
(2) For Level 2 ground motion, the importance of the structure must be taken into account and the seismic resistance of these structures must be considered.

そして、前記構造物の重要度は、１）構造物が損傷を受けた場合の人命・生存にあたえる影響度合、２）避難・救援・救急活動と二次災害防止活動にあたえる影響度合、３）地域の生活機能と経済活動にあたえる影響度合、４）都市機能の早期復旧にあたえる影響度合および復旧の難易度等、を総合して決定されるものとなる。 The importance of the structure is as follows: 1) the degree of impact on the life and survival when the structure is damaged, 2) the degree of impact on the evacuation / rescue / rescue and secondary disaster prevention activities, 3) The degree of impact on local living functions and economic activities, and 4) the degree of impact on early restoration of urban functions and the degree of difficulty in restoration, etc. are determined in a comprehensive manner.

例えば構造物基礎の耐震性能においては、レベル１地震動に対しては液状化を発生させないことを一応の原則とし、レベル２地震動に対しては上部および地中構造に重大な損傷が発生しないことを耐震性能の目標としている。 For example, in the seismic performance of structural foundations, it is assumed that liquefaction will not occur for Level 1 ground motion, and that there will be no significant damage to the upper and underground structures for Level 2 ground motion. The target is seismic performance.

しかし、地盤の液状化に対しては地盤改良によって液状化防止対策を講じることを基本とするのみであり、地盤液状化と免震性との密接な関係性があることは過去長い間知られることがなかった。 However, it has been known for a long time that there is a close relationship between ground liquefaction and seismic isolation, since ground liquefaction is only based on measures to prevent liquefaction by ground improvement. It never happened.

しかしながら近年、地盤が液状化すると地盤の剛性は著しく低下するので，地表の加速度応答は極端に低下し、液状化地盤が逆にいわゆる免震層的な役割を果たすのではないかとの議論が論じられるに至った。 However, in recent years, when the ground is liquefied, the rigidity of the ground is remarkably reduced, so the acceleration response of the ground surface is extremely lowered, and there is a discussion that the liquefied ground may play a role of a so-called seismic isolation layer. It came to be.

事実、過去に生じた地震では、ある構造物（あるアパート）が液状化により大きく傾斜したが、上部構造はまったく無傷であったことがある。 In fact, in an earthquake that occurred in the past, a certain structure (a certain apartment) was greatly inclined due to liquefaction, but the superstructure was completely intact.

この構造物は全部で８棟あったが、当時外出していた方がほとんどであったこともありケガ人は一人も出なかったとされている。 There were 8 buildings in all, but it was said that there were no injuries because some of them were out.

この建物の底を見せるまでに大きく転倒した前記構造物の住人は、地震の間、階段を這うように屋上へ上がったこと、屋上に出て傾斜するのに５分程度要したことを証言している。 The resident of the structure, who had fallen greatly before showing the bottom of this building, testified that during the earthquake, he went up to the roof like a staircase and took about 5 minutes to get out and incline. ing.

人命に対する重要度が特に高いと考えられる住居において、上部構造物の破壊や人命といった点で、同じ地震で最初のぐらっとした揺れとともに家が崩れ死傷者が出た事例と比較し、この構造物は地盤の液状化がむしろ幸いした事例と捉えることができるのである。 Compared to the case where the house collapsed and the casualties were injured in the same earthquake in the dwelling considered to be particularly important for human life, in terms of destruction of the upper structure and human life, The liquefaction of the ground can be regarded as a fortunate example.

また、他の地震の被害調査では、地盤は激しく液状化したと考えられる地点で、構造物に沈下や傾斜が生じてはいるが、上部構造物自体にはなんら被害が生じていないとの光景を良く見かけたとされている。 In another earthquake damage survey, the ground is considered to have been liquefied violently, and the structure has subsided or tilted, but the upper structure itself has not been damaged at all. It is said that it was seen well.

勿論、地盤が液状化した場合には、前記構造物の事例のように構造物自体に何ら損傷を伴わなくても大きな変形が生じる場合が一般的であり、このような変形が致命的な被害となる構造物も多いとは考えられる。 Of course, when the ground is liquefied, as in the case of the above structure, it is common that a large deformation occurs without any damage to the structure itself, and such deformation is fatal damage. It is thought that there are many structures that become.

しかしながら前述したように、種々の構造物に対して、地盤の液状化がどのように影響をあたえるかは重要な問題なのである。 However, as described above, how the liquefaction of the ground affects various structures is an important issue.

であるのに、レベル２地震動のような大きな地震で、液状化と構造物被害との関係はあまり明確にされていないのも実情である。 However, it is a fact that the relationship between liquefaction and structural damage has not been clarified in large earthquakes such as Level 2 ground motion.

また、地盤液状化の評価法についても見直しが行われており、ある液状化判定法によれば、地震外力が増加した分、中密な地盤も液状化する（液状化抵抗率ＦＬが１．０を下回る）判定結果となる場合が多いとされている。 Also, the ground liquefaction evaluation method has been reviewed, and according to a certain liquefaction judgment method, the solid ground is liquefied as the earthquake external force increases (liquefaction resistivity FL is 1.). It is said that there are many cases where the determination result is less than 0).

一般的に現行の設計法では、液状化が生じる地盤と判定された場合には、何らかの液状化対策を行うか、構造物基礎を強化するなどそれなりの対策が必要となる。 In general, in the current design method, when it is determined that the ground is liquefied, some countermeasures such as some liquefaction countermeasures or strengthening of the structure foundation are required.

しかし、地震の発生確率としてはレベル１地震動に比べ、はるかに低い確率で発生するレベル２地震動に対し、同じ液状化抵抗率であるとして、レベル１地震動と同じレベルで液状化対策を行うのは必ずしも合理的ではないのではないかとも考えられる。 However, as for the probability of earthquake occurrence, liquefaction countermeasures at the same level as Level 1 ground motion are taken as the same liquefaction resistance against Level 2 ground motion that occurs at a much lower probability than Level 1 ground motion. It may not be reasonable.

また，たとえ、同じ液状化抵抗率であっても、地盤の挙動やその液状化が構造物に与える影響は異なるものと考えられ、特に、中密な地盤における構造物被害については不明な点が多いのも事実である。 In addition, even if the liquefaction resistivity is the same, the behavior of the ground and the effect of the liquefaction on the structure are considered to be different. In particular, there are unclear points regarding structural damage in the dense ground. It is also true that there are many.

すなわち、前述のように地盤の液状化しやすさが、そのまま構造物被害の大きさに比例していることを意味しているわけではないので、このような地盤の液状化しやすさとレベル２地震動における構造物被害との関係をより明らかにする必要もある。
しかして、過去の生じた地震において、数多くの被害調査が実施され、構造物の調査や地盤の液状化についても多くの調査が実施されている。 In other words, as described above, the ease of ground liquefaction does not mean that it is directly proportional to the magnitude of structural damage. It is also necessary to clarify the relationship with structural damage.
In the past earthquakes, many damage investigations have been carried out, and many investigations have been carried out regarding the investigation of structures and liquefaction of the ground.

ただし、液状化とともに、地盤条件、構造物基礎、上部構造といった全体系を捉えた調査結果がほとんど見あたらないのも事実である。
ここで、
（１）液状化が種々の構造物被害に与えた影響（主に、液状化による免震層的な効果がどのようなものであったか）。
（２）地盤条件や地震動が種々の構造物被害や液状化に与えた影響（主に、中密な地盤における被害はどのようなものであったか）。
（３）過去の地震における液状化による人的被害。 However, with liquefaction, it is also true that there are few survey results that capture the entire system such as ground conditions, structure foundations, and superstructure.
here,
(1) The impact of liquefaction on various structural damages (mainly what the seismic isolation layer effect of liquefaction was).
(2) Effects of ground conditions and earthquake motion on various structural damages and liquefaction (mainly what kind of damage was done on the dense ground).
(3) Human damage due to liquefaction in past earthquakes.

レベル２地震動であったと考えられる地震を仮にマグニチュード6．5以上の内陸直下型地震とすると，このような地震は日本においても過去数回起きている。 If an earthquake that is thought to have been Level 2 ground motion is an inland direct earthquake with a magnitude of 6.5 or more, such an earthquake has occurred several times in Japan.

また、海外では過去10年以内で数回起きており、これらの地震ではいずれも地盤の液状化が発生している。 In addition, it has happened several times within the past 10 years overseas, and the ground has liquefied in all of these earthquakes.

このように、いわゆるレベル２地震動が発生し、しかも液状化が発生した地震は決して少なくないが、ここでは調査対象を一番情報が集めやすいという理由で、基本的に日本で起きた近年の大型地震とし、部分的に補足として他の地震についても調査が行われた。 In this way, so-called Level 2 earthquake motion has occurred and liquefaction has occurred in many cases, but here, the recent large-scale earthquake that occurred in Japan was basically the reason for collecting the most information. Surveys were conducted on other earthquakes as part of the earthquake.

そして、この地震では、（ａ）沖積低地が少なく海岸埋立地における液状化が圧倒的に多かったこと，（ｂ）液状化した地盤の多くは、まさ土による埋立地盤であったこと、が特徴とされており、このような特殊性を持った地震被害調査結果であった。 And in this earthquake, (a) there were few alluvial lowlands, and the liquefaction in the coastal landfill was overwhelmingly large, and (b) most of the liquefied ground was the landfill board made of masa soil. It was the result of a survey of earthquake damage with such special characteristics.

被害調査は、建築物、道路橋、タンク、鉄道橋および人的被害について実施されたが、この調査によると、海岸埋立地のほぼ全域で液状化が生じたことが明白となった。さらに、これらのなかでも、ある海岸埋立地は、山から採取された、まさ土によって埋め立てられていることが確認された。 Damage surveys were conducted on buildings, road bridges, tanks, railway bridges, and human damage. According to this survey, it was clear that liquefaction occurred almost throughout the coastal landfill. Furthermore, among these, it was confirmed that a certain coastal reclaimed land was reclaimed by masa soil taken from the mountain.

また、液状化が多数確認されている地域は、沖積低地がきわめて狭い地形となっている地域であった。 In addition, areas where many liquefactions were confirmed were areas where alluvial lowlands were extremely narrow.

したがって、この地震の調査範囲における液状化の特徴としては、
（１）海岸埋立地における液状化が圧倒的に多かったこと。
（２）液状化した地盤の多くはまさ土による埋立地盤であることが挙げられる。 Therefore, as a characteristic of liquefaction in the survey area of this earthquake,
(1) The liquefaction in the coastal landfill was overwhelmingly large.
(2) Most of the ground that has been liquefied is a landfill board made of masa soil.

そして、近年では、前記のように、「液状化に関する地盤防災の研究」がより一層活発となり、かつそこで得られた各種情報にヒントを得て、地震時に地盤が液状化することで当該地盤が逆に免震地盤層となるとの状況が確認された。 In recent years, as described above, “study on ground disaster prevention related to liquefaction” has become even more active, and various information obtained there has been used as a hint. On the contrary, the situation that it becomes a seismic isolation ground layer was confirmed.

そして、近年、地震で生じる液状化や地盤の軟化現象を積極的に容認し、基盤からの地震力を地盤剛性の低下による免震効果で地震動の低減に利用するとのことが提案されるに至った（特許公開平１１−１８１７５５）。 In recent years, it has been proposed to actively accept the liquefaction and softening phenomena of the ground caused by earthquakes, and to use the seismic force from the base to reduce the ground motion by the seismic isolation effect due to the decrease in ground rigidity. (Patent Publication No. 11-181755).

更に、これを利用した工法も提案されている（特許公開２００３−２０６５９，特許公開２０００−９６５８０，特許公開平１１−３１５５４４，特許公開平１０−２９２３９１，特許公開平６−１０８４７７）。 Further, a construction method using this has been proposed (Patent Publication 2003-20659, Patent Publication 2000-96580, Patent Publication Hei 11-315544, Patent Publication Hei 10-292391, Patent Publication Hei 6-108477).

このうち、特許公開平１１−１８１７５５号公報には、軟弱地盤対策において地盤改良を所定の深度まで改良せず、未改良部分を故意に残し軟弱層とすることで免震構造を構築するとしている発明が示されている。
特許公開平１１−１８１７５５号公報 Among these, in Japanese Patent Publication No. 11-181755, it is said that the seismic isolation structure is constructed by leaving the unimproved part intentionally and making it a soft layer without improving the ground improvement to a predetermined depth in the countermeasure for the soft ground. The invention is shown.
Japanese Patent Publication No. 11-181755

しかして、本発明は前記従来からの提案をさらに進化させて創案されたものであり、積極的な地盤改良を行わずとも地表近くの層を非軟弱地盤である改良地盤となしえ、しかもその下層を所定範囲軟弱地盤として存置し、当該軟弱地盤を免震層とすることにより、より容易に改良地盤、かつ免震地盤が形成でき、かつよりその形成の実現性が高く、しかも低コストで実現できる免震層が形成できる免震地盤形成方法を提供することを目的とするものである。 Thus, the present invention was created by further evolving the above-mentioned conventional proposals, and the layer near the surface can be formed as an improved ground which is a non-soft ground without aggressive ground improvement, and the By leaving the lower layer as a predetermined range soft ground and making the soft ground as a seismic isolation layer, improved ground and seismic isolation ground can be formed more easily, and its formation is more feasible and at low cost. The object is to provide a seismic isolation ground formation method that can form a seismic isolation layer that can be realized.

本発明による免震地盤形成方法は、
軟弱地盤上での構造物建設に先立ち、前記軟弱地盤上に所定重量の荷重物を所定時間載置し、その後前記荷重物を撤去して生ずる過圧密履歴作用を用いて、前記軟弱地盤表面部より所定厚みを有した非軟弱地盤層を形成すると共に、該非軟弱地盤層の下層には液状化層となる軟弱地盤層を残置し、該軟弱地盤層を免震層とする免震地盤形成方法であり、
前記軟弱地盤の土質測定値であるＮ値を用いて、当該軟弱地盤の液状化抵抗値Ｒを測定し、
当該軟弱地盤におけるレベル２地震動の地震時せん断応力比Ｌを測定し、
前記液状化抵抗値Ｒとレベル２地震動の地震時せん断応力比Ｌの測定値を用いて前記軟弱地盤のレベル２地震動に対する液状化抵抗率ＦＬを測定し、
前記レベル２地震動に対する液状化抵抗率ＦＬの測定値を用いて前記軟弱地盤のレベル２地震動に対する液状化指数ＰＬを測定し、
前記レベル２地震動に対する液状化指数ＰＬと、過去の地震被害事例や構造物の重要度などに基づき決定される目標液状化指数ＰＬ _Ｔとを比較し、
前記当該軟弱地盤におけるレベル２地震動に対する液状化指数ＰＬが目標液状化指数ＰＬ _Ｔの値より大きいときに、前記液状化指数ＰＬを算出する式と土質の液状化抵抗増加係数ｎの値を用いて、ＰＬ−ｑ（当該軟弱地盤における液状化指数ＰＬの大きさを縦軸に表し、盛土荷重ｑの大きさを横軸に表して得られた、盛土荷重の大小により生ずる液状化指数ＰＬの変化を表した曲線：荷重物の目標重量値の算出用）の関係図を作製し、
前記ＰＬ−ｑの関係図から、目標液状化指数ＰＬ _Ｔに対応する荷重物の目標重量値が算出できる、
ことを特徴とし、
または、
軟弱地盤上での構造物建設に先立ち、前記軟弱地盤上に所定重量の荷重物を所定時間載置し、その後前記荷重物を撤去して生ずる過圧密履歴作用を用いて、前記軟弱地盤表面部より所定厚みを有した非軟弱地盤層を形成すると共に、該非軟弱地盤層の下層には液状化層となる軟弱地盤層を残置し、該軟弱地盤層を免震層とする免震地盤形成方法であり、
前記軟弱地盤の土質測定値であるＮ値を用いて、当該軟弱地盤の液状化抵抗値Ｒを測定し、
当該軟弱地盤におけるレベル２地震動の地震時せん断応力比Ｌを測定し、
前記液状化抵抗値Ｒとレベル２地震動の地震時せん断応力比Ｌの測定値を用いて前記軟弱地盤のレベル２地震動に対する液状化抵抗率ＦＬを測定し、
前記レベル２地震動に対する液状化抵抗率ＦＬの測定値を用いて前記軟弱地盤のレベル２地震動に対する液状化指数ＰＬを測定し、
前記レベル２地震動に対する液状化指数ＰＬと、過去の地震被害事例や構造物の重要度などに基づき決定される目標液状化指数ＰＬ _Ｔとを比較し、
前記レベル２地震動に対する液状化指数ＰＬが目標液状化指数ＰＬ _Ｔの値より大きいときに、前記液状化指数ＰＬを算出する式と土質の液状化抵抗増加係数ｎの値を用いて、ＰＬ−ｑ（液状化指数ＰＬの大きさを縦軸に表し、盛土荷重ｑの大きさを横軸に表して得られた、盛土荷重の大小により生ずる液状化指数ＰＬの変化を表した曲線：荷重物の目標重量値の算出用）の関係図を作製し、
前記ＰＬ−ｑの関係図から、目標液状化指数ＰＬ _Ｔに対応する荷重物の目標重量値を算出し、
かつ、前記軟弱地盤の土質を測定して得られた土質データにより前記目標重量値の載置時間を算出する、
ことを特徴とし、
または、
軟弱地盤上での構造物建設に先立ち、前記軟弱地盤上に所定重量の荷重物を所定時間載置し、その後前記荷重物を撤去して生ずる過圧密履歴作用を用いて、前記軟弱地盤表面部より所定厚みを有した非軟弱地盤層を形成すると共に、該非軟弱地盤層の下層には液状化層となる軟弱地盤層を残置し、該軟弱地盤層を免震層とする免震地盤形成方法であり、
前記軟弱地盤の土質測定値であるＮ値を基に当該軟弱地盤における土質粒度の影響を考慮して補正したＮａ値を求め、該Ｎａ値を用いて当該軟弱地盤の液状化抵抗値Ｒを測定し、
当該軟弱地盤におけるレベル２地震動の地震時せん断応力比Ｌを測定し、
前記液状化抵抗値Ｒとレベル２地震動の地震時せん断応力比Ｌの測定値を用いて前記軟弱地盤のレベル２地震動に対する液状化抵抗率ＦＬを測定し、
前記レベル２地震動に対する液状化抵抗率ＦＬの測定値を用いて前記軟弱地盤のレベル２地震動に対する液状化指数ＰＬを測定し、
前記レベル２地震動に対する液状化指数ＰＬと、過去の地震被害事例や構造物の重要度などに基づき決定される目標液状化指数ＰＬ _Ｔとを比較し、
前記当該軟弱地盤におけるレベル２地震動に対する液状化指数ＰＬが目標液状化指数ＰＬ _Ｔの値より大きいときに、前記液状化指数ＰＬを算出する式と土質の液状化抵抗増加係数ｎの値を用いて、ＰＬ−ｑ（当該軟弱地盤における液状化指数ＰＬの大きさを縦軸に表し、盛土荷重ｑの大きさを横軸に表して得られた、盛土荷重の大小により生ずる液状化指数ＰＬの変化を表した曲線：荷重物の目標重量値の算出用）の関係図を作製し、
前記ＰＬ−ｑの関係図から、目標液状化指数ＰＬ _Ｔに対応する荷重物の目標重量値が算出できる、
ことを特徴とし、
または、
軟弱地盤上での構造物建設に先立ち、前記軟弱地盤上に所定重量の荷重物を所定時間載置し、その後前記荷重物を撤去して生ずる過圧密履歴作用を用いて、前記軟弱地盤表面部より所定厚みを有した非軟弱地盤層を形成すると共に、該非軟弱地盤層の下層には液状化層となる軟弱地盤層を残置し、該軟弱地盤層を免震層とする免震地盤形成方法であり、
前記軟弱地盤の土質測定値であるＮ値を基に当該軟弱地盤における土質粒度の影響を考慮して補正したＮａ値を求め、該Ｎａ値を用いて当該軟弱地盤の液状化抵抗値Ｒを測定し、
当該軟弱地盤におけるレベル２地震動の地震時せん断応力比Ｌを測定し、
前記液状化抵抗値Ｒとレベル２地震動の地震時せん断応力比Ｌの測定値を用いて前記軟弱地盤のレベル２地震動に対する液状化抵抗率ＦＬを測定し、
前記レベル２地震動に対する液状化抵抗率ＦＬの測定値を用いて前記軟弱地盤のレベル２地震動に対する液状化指数ＰＬを測定し、
前記レベル２地震動に対する液状化指数ＰＬと、過去の地震被害事例や構造物の重要度などに基づき決定される目標液状化指数ＰＬ _Ｔとを比較し、
前記レベル２地震動に対する液状化指数ＰＬが目標液状化指数ＰＬ _Ｔの値より大きいときに、前記液状化指数ＰＬを算出する式と土質の液状化抵抗増加係数ｎの値を用いて、ＰＬ−ｑ（液状化指数ＰＬの大きさを縦軸に表し、盛土荷重ｑの大きさを横軸に表して得られた、盛土荷重の大小により生ずる液状化指数ＰＬの変化を表した曲線：荷重物の目標重量値の算出用）の関係図を作製し、
前記ＰＬ−ｑの関係図から、目標液状化指数ＰＬ _Ｔに対応する荷重物の目標重量値を算出し、
かつ、前記軟弱地盤の土質を測定して得られた土質データにより前記目標重量値の載置時間を算出する、
ことを特徴とし、
または、
軟弱地盤上での構造物建設に先立ち、前記軟弱地盤上に所定重量の荷重物を所定時間載置し、その後前記荷重物を撤去して生ずる過圧密履歴作用を用いて、前記軟弱地盤表面部より所定厚みを有した非軟弱地盤層を形成すると共に、該非軟弱地盤層の下層には液状化層となる軟弱地盤層を残置し、該軟弱地盤層を免震層とする免震地盤形成方法であり、
前記軟弱地盤の土質測定値であるＮ値を用いて、当該軟弱地盤の液状化抵抗値Ｒを測定し、
当該軟弱地盤におけるレベル１地震動及びレベル２地震動の地震時せん断応力比Ｌを各々測定し、
前記液状化抵抗値Ｒと前記レベル１地震動及びレベル２地震動の地震時せん断応力比Ｌの測定値を用いて前記軟弱地盤のレベル１地震動及びレベル２地震動に対する液状化抵抗率ＦＬを各々測定し、
前記液状化抵抗率ＦＬの測定値を用いて前記軟弱地盤のレベル１地震動及びレベル２地震動に対する液状化指数ＰＬを各々測定し、
前記レベル１地震動に対する液状化指数ＰＬと過去の地震被害事例や構造物の重要度などに基づき決定される液状化発生条件液状化指数ＰＬ _Ｌとを比較し、
前記レベル１地震動に対する液状化指数ＰＬの値が前記液状化発生条件液状化指数ＰＬ _Ｌの値よりも大なるときには、前記レベル２地震動に対する液状化指数ＰＬと、過去の地震被害事例や構造物の重要度などに基づき決定される目標液状化指数ＰＬ _Ｔとを比較し、
前記当該軟弱地盤におけるレベル２地震動に対する液状化指数ＰＬが目標液状化指数ＰＬ _Ｔの値より大きいときに、前記液状化指数ＰＬを算出する式と土質の液状化抵抗増加係数ｎの値を用いて、ＰＬ−ｑ（当該軟弱地盤における液状化指数ＰＬの大きさを縦軸に表し、盛土荷重ｑの大きさを横軸に表して得られた、盛土荷重の大小により生ずる液状化指数ＰＬの変化を表した曲線：荷重物の目標重量値の算出用）の関係図を作製し、
前記ＰＬ−ｑの関係図から、目標液状化指数ＰＬ _Ｔに対応する荷重物の目標重量値が算出できる、
ことを特徴とし、
または、
軟弱地盤上での構造物建設に先立ち、前記軟弱地盤上に所定重量の荷重物を所定時間載置し、その後前記荷重物を撤去して生ずる過圧密履歴作用を用いて、前記軟弱地盤表面部より所定厚みを有した非軟弱地盤層を形成すると共に、該非軟弱地盤層の下層には液状化層となる軟弱地盤層を残置し、該軟弱地盤層を免震層とする免震地盤形成方法であり、
前記軟弱地盤の土質測定値であるＮ値を用いて、当該軟弱地盤の液状化抵抗値Ｒを測定し、
当該軟弱地盤におけるレベル１地震動及びレベル２地震動の地震時せん断応力比Ｌを各々測定し、
前記液状化抵抗値Ｒと前記レベル１地震動及びレベル２地震動の地震時せん断応力比Ｌの測定値を用いて前記軟弱地盤のレベル１地震動及びレベル２地震動に対する液状化抵抗率ＦＬを各々測定し、
前記液状化抵抗率ＦＬの測定値を用いて前記軟弱地盤のレベル１地震動及びレベル２地震動に対する液状化指数ＰＬを各々測定し、
前記レベル１地震動に対する液状化指数ＰＬと過去の地震被害事例や構造物の重要度などに基づき決定される液状化発生条件液状化指数ＰＬ _Ｌとを比較し、
前記レベル１地震動に対する液状化指数ＰＬの値が前記液状化発生条件液状化指数ＰＬ _Ｌの値よりも大なるときには、前記レベル２地震動に対する液状化指数ＰＬと、過去の地震被害事例や構造物の重要度などに基づき決定される目標液状化指数ＰＬ _Ｔとを比較し、
前記当該軟弱地盤におけるレベル２地震動に対する液状化指数ＰＬが目標液状化指数ＰＬ _Ｔの値より大きいときに、前記液状化指数ＰＬを算出する式と土質の液状化抵抗増加係数ｎの値を用いて、ＰＬ−ｑ（当該軟弱地盤における液状化指数ＰＬの大きさを縦軸に表し、盛土荷重ｑの大きさを横軸に表して得られた、盛土荷重の大小により生ずる液状化指数ＰＬの変化を表した曲線：荷重物の目標重量値の算出用）の関係図を作製し、
前記ＰＬ−ｑの関係図から、目標液状化指数ＰＬ _Ｔに対応する荷重物の目標重量値が算出し、
かつ、前記軟弱地盤の土質を測定して得られた土質データにより前記目標重量値の載置時間を算出する、
ことを特徴とし、
または、
軟弱地盤上での構造物建設に先立ち、前記軟弱地盤上に所定重量の荷重物を所定時間載置し、その後前記荷重物を撤去して生ずる過圧密履歴作用を用いて、前記軟弱地盤表面部より所定厚みを有した非軟弱地盤層を形成すると共に、該非軟弱地盤層の下層には液状化層となる軟弱地盤層を残置し、該軟弱地盤層を免震層とする免震地盤形成方法であり、
前記軟弱地盤の土質測定値であるＮ値を基に、当該軟弱地盤における土質粒度の影響を考慮して補正したＮａ値を求め、該Ｎａ値を用いて当該軟弱地盤の液状化抵抗値Ｒを測定し、
当該軟弱地盤におけるレベル１地震動及びレベル２地震動の地震時せん断応力比Ｌを各々測定し、
前記液状化抵抗値Ｒと前記レベル１地震動及びレベル２地震動の地震時せん断応力比Ｌの測定値を用いて前記軟弱地盤のレベル１地震動及びレベル２地震動に対する液状化抵抗率ＦＬを各々測定し、
前記液状化抵抗率ＦＬの測定値を用いて前記軟弱地盤のレベル１地震動及びレベル２地震動に対する液状化指数ＰＬを各々測定し、
前記レベル１地震動に対する液状化指数ＰＬと過去の地震被害事例や構造物の重要度などに基づき決定される液状化発生条件液状化指数ＰＬ _Ｌとを比較し、
前記レベル１地震動に対する液状化指数ＰＬの値が前記液状化発生条件液状化指数ＰＬ _Ｌの値よりも大なるときには、前記レベル２地震動に対する液状化指数ＰＬと、過去の地震被害事例や構造物の重要度などに基づき決定される目標液状化指数ＰＬ _Ｔとを比較し、
前記当該軟弱地盤におけるレベル２地震動に対する液状化指数ＰＬが目標液状化指数ＰＬ _Ｔの値より大きいときに、前記液状化指数ＰＬを算出する式と土質の液状化抵抗増加係数ｎの値を用いて、ＰＬ−ｑ（当該軟弱地盤における液状化指数ＰＬの大きさを縦軸に表し、盛土荷重ｑの大きさを横軸に表して得られた、盛土荷重の大小により生ずる液状化指数ＰＬの変化を表した曲線：荷重物の目標重量値の算出用）の関係図を作製し、
前記ＰＬ−ｑの関係図から、目標液状化指数ＰＬ _Ｔに対応する荷重物の目標重量値が算出できる、
ことを特徴とし、
または、
軟弱地盤上での構造物建設に先立ち、前記軟弱地盤上に所定重量の荷重物を所定時間載置し、その後前記荷重物を撤去して生ずる過圧密履歴作用を用いて、前記軟弱地盤表面部より所定厚みを有した非軟弱地盤層を形成すると共に、該非軟弱地盤層の下層には液状化層となる軟弱地盤層を残置し、該軟弱地盤層を免震層とする免震地盤形成方法であり、
前記軟弱地盤の土質測定値であるＮ値を基に、当該軟弱地盤における土質粒度の影響を考慮して補正したＮａ値を求め、該Ｎａ値を用いて当該軟弱地盤の液状化抵抗値Ｒを測定し、
当該軟弱地盤におけるレベル１地震動及びレベル２地震動の地震時せん断応力比Ｌを各々測定し、
前記液状化抵抗値Ｒと前記レベル１地震動及びレベル２地震動の地震時せん断応力比Ｌの測定値を用いて前記軟弱地盤のレベル１地震動及びレベル２地震動に対する液状化抵抗率ＦＬを各々測定し、
前記液状化抵抗率ＦＬの測定値を用いて前記軟弱地盤のレベル１地震動及びレベル２地震動に対する液状化指数ＰＬを各々測定し、
前記レベル１地震動に対する液状化指数ＰＬと過去の地震被害事例や構造物の重要度などに基づき決定される液状化発生条件液状化指数ＰＬ _Ｌとを比較し、
前記レベル１地震動に対する液状化指数ＰＬの値が前記液状化発生条件液状化指数ＰＬ _Ｌの値よりも大なるときには、前記レベル２地震動に対する液状化指数ＰＬと、過去の地震被害事例や構造物の重要度などに基づき決定される目標液状化指数ＰＬ _Ｔとを比較し、
前記当該軟弱地盤におけるレベル２地震動に対する液状化指数ＰＬが目標液状化指数ＰＬ _Ｔの値より大きいときに、前記液状化指数ＰＬを算出する式と土質の液状化抵抗増加係数ｎの値を用いて、ＰＬ−ｑ（当該軟弱地盤における液状化指数ＰＬの大きさを縦軸に表し、盛土荷重ｑの大きさを横軸に表して得られた、盛土荷重の大小により生ずる液状化指数ＰＬの変化を表した曲線：荷重物の目標重量値の算出用）の関係図を作製し、
前記ＰＬ−ｑの関係図から、目標液状化指数ＰＬ _Ｔに対応する荷重物の目標重量値が算出し、
かつ、前記軟弱地盤の土質を測定して得られた土質データにより前記目標重量値の載置時間を算出する、
ことを特徴とし、
または、
前記目標液状化指数ＰＬ_Ｔは過去のデータを算出して更新可能とされた、
ことを特徴とし、
または、
前記目標重量載置時間の算出は、前記軟弱地盤の沈下量に基づいて算出可能とされた、
ことを特徴とするものである。
The seismic isolation ground formation method according to the present invention includes:
Prior to the construction of the structure on the soft ground, a load object having a predetermined weight is placed on the soft ground for a predetermined time, and then the over-consolidation history effect generated by removing the load object is used, and the soft ground surface portion A non-soft ground layer having a predetermined thickness is formed, and a soft ground layer that becomes a liquefied layer is left in a lower layer of the non-soft ground layer, and the soft ground layer is used as a base isolation layer. And
Measure the liquefaction resistance value R of the soft ground using the N value which is the soil measurement value of the soft ground,
Measure the shear stress ratio L at the time of earthquake of level 2 ground motion in the soft ground,
Measure the liquefaction resistivity FL against level 2 ground motion of the soft ground using the measured value of the liquefaction resistance value R and the shear stress ratio L during earthquake of level 2 ground motion,
Using the measured value of the liquefaction resistivity FL for the level 2 earthquake motion, the liquefaction index PL for the level 2 earthquake motion of the soft ground is measured,
Compares the liquefaction index PL with respect to the level 2 ground motion, the target liquefaction index PL _T which is determined on the basis of such importance of the past earthquakes damage case and structures,
When liquefaction index PL for the level 2 earthquake motion in the said soft ground is greater than the value of the target liquefaction index PL _T, using the formula and values of liquefaction resistance increase coefficient n of soil for calculating the liquefaction index PL , PL-q (change in the liquefaction index PL caused by the magnitude of the embankment load obtained by expressing the magnitude of the liquefaction index PL in the soft ground on the vertical axis and the magnitude of the embankment load q on the horizontal axis Curve): for calculating the target weight value of the load)
From the relationship diagram of the PL-q, target weight value of the load object corresponding to the target liquefaction index PL _T can be calculated,
It is characterized by
Or
Prior to the construction of the structure on the soft ground, a load object having a predetermined weight is placed on the soft ground for a predetermined time, and then the over-consolidation history effect generated by removing the load object is used, and the soft ground surface portion A non-soft ground layer having a predetermined thickness is formed, and a soft ground layer that becomes a liquefied layer is left in a lower layer of the non-soft ground layer, and the soft ground layer is used as a base isolation layer. And
Measure the liquefaction resistance value R of the soft ground using the N value which is the soil measurement value of the soft ground,
Measure the shear stress ratio L at the time of earthquake of level 2 ground motion in the soft ground,
Measure the liquefaction resistivity FL against level 2 ground motion of the soft ground using the measured value of the liquefaction resistance value R and the shear stress ratio L during earthquake of level 2 ground motion,
Using the measured value of the liquefaction resistivity FL for the level 2 earthquake motion, the liquefaction index PL for the level 2 earthquake motion of the soft ground is measured,
Compares the liquefaction index PL with respect to the level 2 ground motion, the target liquefaction index PL _T which is determined on the basis of such importance of the past earthquakes damage case and structures,
When liquefaction index PL with respect to the level 2 earthquake motion is greater than the value of the target liquefaction index PL _T, using the formula and values of liquefaction resistance increase coefficient n of soil for calculating the liquefaction index PL, PL-q (A curve representing the change in the liquefaction index PL caused by the magnitude of the embankment load, obtained by expressing the magnitude of the liquefaction index PL on the vertical axis and the magnitude of the embankment load q on the horizontal axis: For the calculation of the target weight value)
From the relationship diagram of the PL-q, and calculates a target weight value of the load object corresponding to the target liquefaction index PL _T,
And calculating the placement time of the target weight value by soil data obtained by measuring the soil of the soft ground,
It is characterized by
Or
Prior to the construction of the structure on the soft ground, a load object having a predetermined weight is placed on the soft ground for a predetermined time, and then the over-consolidation history effect generated by removing the load object is used, and the soft ground surface portion A non-soft ground layer having a predetermined thickness is formed, and a soft ground layer that becomes a liquefied layer is left in a lower layer of the non-soft ground layer, and the soft ground layer is used as a base isolation layer. And
Based on the N value which is the soil measurement value of the soft ground, a corrected Na value is calculated in consideration of the influence of soil grain size in the soft ground, and the liquefaction resistance value R of the soft ground is measured using the Na value. And
Measure the shear stress ratio L at the time of earthquake of level 2 ground motion in the soft ground,
Measure the liquefaction resistivity FL against level 2 ground motion of the soft ground using the measured value of the liquefaction resistance value R and the shear stress ratio L during earthquake of level 2 ground motion,
Using the measured value of the liquefaction resistivity FL for the level 2 earthquake motion, the liquefaction index PL for the level 2 earthquake motion of the soft ground is measured,
Compares the liquefaction index PL with respect to the level 2 ground motion, the target liquefaction index PL _T which is determined on the basis of such importance of the past earthquakes damage case and structures,
When liquefaction index PL for the level 2 earthquake motion in the said soft ground is greater than the value of the target liquefaction index PL _T, using the formula and values of liquefaction resistance increase coefficient n of soil for calculating the liquefaction index PL , PL-q (change in the liquefaction index PL caused by the magnitude of the embankment load obtained by expressing the magnitude of the liquefaction index PL in the soft ground on the vertical axis and the magnitude of the embankment load q on the horizontal axis Curve): for calculating the target weight value of the load)
From the relationship diagram of the PL-q, target weight value of the load object corresponding to the target liquefaction index PL _T can be calculated,
It is characterized by
Or
Prior to the construction of the structure on the soft ground, a load object having a predetermined weight is placed on the soft ground for a predetermined time, and then the over-consolidation history effect generated by removing the load object is used, and the soft ground surface portion A non-soft ground layer having a predetermined thickness is formed, and a soft ground layer that becomes a liquefied layer is left in a lower layer of the non-soft ground layer, and the soft ground layer is used as a base isolation layer. And
Based on the N value which is the soil measurement value of the soft ground, a corrected Na value is calculated in consideration of the influence of soil grain size in the soft ground, and the liquefaction resistance value R of the soft ground is measured using the Na value. And
Measure the shear stress ratio L at the time of earthquake of level 2 ground motion in the soft ground,
Measure the liquefaction resistivity FL against level 2 ground motion of the soft ground using the measured value of the liquefaction resistance value R and the shear stress ratio L during earthquake of level 2 ground motion,
Using the measured value of the liquefaction resistivity FL for the level 2 earthquake motion, the liquefaction index PL for the level 2 earthquake motion of the soft ground is measured,
Compares the liquefaction index PL with respect to the level 2 ground motion, the target liquefaction index PL _T which is determined on the basis of such importance of the past earthquakes damage case and structures,
When liquefaction index PL with respect to the level 2 earthquake motion is greater than the value of the target liquefaction index PL _T, using the formula and values of liquefaction resistance increase coefficient n of soil for calculating the liquefaction index PL, PL-q (A curve representing the change in the liquefaction index PL caused by the magnitude of the embankment load, obtained by expressing the magnitude of the liquefaction index PL on the vertical axis and the magnitude of the embankment load q on the horizontal axis: For the calculation of the target weight value)
From the relationship diagram of the PL-q, and calculates a target weight value of the load object corresponding to the target liquefaction index PL _T,
And calculating the placement time of the target weight value by soil data obtained by measuring the soil of the soft ground,
It is characterized by
Or
Prior to the construction of the structure on the soft ground, a load object having a predetermined weight is placed on the soft ground for a predetermined time, and then the over-consolidation history effect generated by removing the load object is used, and the soft ground surface portion A non-soft ground layer having a predetermined thickness is formed, and a soft ground layer that becomes a liquefied layer is left in a lower layer of the non-soft ground layer, and the soft ground layer is used as a base isolation layer. And
Measure the liquefaction resistance value R of the soft ground using the N value which is the soil measurement value of the soft ground,
Measure the shear stress ratio L at the time of earthquake of Level 1 ground motion and Level 2 ground motion in the soft ground,
Measure the liquefaction resistivity FL against level 1 and level 2 ground motions of the soft ground using the liquefaction resistance value R and the measured shear stress ratio L of the level 1 and level 2 ground motions, respectively.
Using the measured value of the liquefaction resistivity FL, the liquefaction index PL for the level 1 ground motion and the level 2 ground motion of the soft ground is respectively measured.
The liquefaction index PL for the level 1 earthquake motion is compared with the liquefaction occurrence condition liquefaction index PL _L determined based on past earthquake damage cases and importance of structures ,
When the value of the liquefaction index PL with respect to the level 1 earthquake motion larger becomes than the value of the liquefaction occurrence condition liquefaction index PL _L includes a liquefaction index PL with respect to the level 2 ground motion, the past earthquakes damage case and structures comparing the target liquefaction index PL _T which is determined on the basis of such importance,
When liquefaction index PL for the level 2 earthquake motion in the said soft ground is greater than the value of the target liquefaction index PL _T, using the formula and values of liquefaction resistance increase coefficient n of soil for calculating the liquefaction index PL , PL-q (change in the liquefaction index PL caused by the magnitude of the embankment load obtained by expressing the magnitude of the liquefaction index PL in the soft ground on the vertical axis and the magnitude of the embankment load q on the horizontal axis Curve): for calculating the target weight value of the load)
From the relationship diagram of the PL-q, target weight value of the load object corresponding to the target liquefaction index PL _T can be calculated,
It is characterized by
Or
Prior to the construction of the structure on the soft ground, a load object having a predetermined weight is placed on the soft ground for a predetermined time, and then the over-consolidation history effect generated by removing the load object is used, and the soft ground surface portion A non-soft ground layer having a predetermined thickness is formed, and a soft ground layer that becomes a liquefied layer is left in a lower layer of the non-soft ground layer, and the soft ground layer is used as a base isolation layer. And
Measure the liquefaction resistance value R of the soft ground using the N value which is the soil measurement value of the soft ground,
Measure the shear stress ratio L at the time of earthquake of Level 1 ground motion and Level 2 ground motion in the soft ground,
Measure the liquefaction resistivity FL against level 1 and level 2 ground motions of the soft ground using the liquefaction resistance value R and the measured shear stress ratio L of the level 1 and level 2 ground motions, respectively.
Using the measured value of the liquefaction resistivity FL, the liquefaction index PL for the level 1 ground motion and the level 2 ground motion of the soft ground is respectively measured.
The liquefaction index PL for the level 1 earthquake motion is compared with the liquefaction occurrence condition liquefaction index PL _L determined based on past earthquake damage cases and importance of structures ,
When the value of the liquefaction index PL with respect to the level 1 earthquake motion larger becomes than the value of the liquefaction occurrence condition liquefaction index PL _L includes a liquefaction index PL with respect to the level 2 ground motion, the past earthquakes damage case and structures comparing the target liquefaction index PL _T which is determined on the basis of such importance,
When liquefaction index PL for the level 2 earthquake motion in the said soft ground is greater than the value of the target liquefaction index PL _T, using the formula and values of liquefaction resistance increase coefficient n of soil for calculating the liquefaction index PL , PL-q (change in the liquefaction index PL caused by the magnitude of the embankment load obtained by expressing the magnitude of the liquefaction index PL in the soft ground on the vertical axis and the magnitude of the embankment load q on the horizontal axis Curve): for calculating the target weight value of the load)
From the relationship diagram of the PL-q, target weight value of the load object corresponding to the target liquefaction index PL _T is calculated,
And calculating the placement time of the target weight value by soil data obtained by measuring the soil of the soft ground,
It is characterized by
Or
Prior to the construction of the structure on the soft ground, a load object having a predetermined weight is placed on the soft ground for a predetermined time, and then the over-consolidation history effect generated by removing the load object is used, and the soft ground surface portion A non-soft ground layer having a predetermined thickness is formed, and a soft ground layer that becomes a liquefied layer is left in a lower layer of the non-soft ground layer, and the soft ground layer is used as a base isolation layer. And
Based on the N value that is the soil measurement value of the soft ground, a corrected Na value is obtained in consideration of the influence of the soil grain size in the soft ground, and the liquefaction resistance value R of the soft ground is calculated using the Na value. Measure and
Measure the shear stress ratio L at the time of earthquake of Level 1 ground motion and Level 2 ground motion in the soft ground,
Measure the liquefaction resistivity FL against level 1 and level 2 ground motions of the soft ground using the liquefaction resistance value R and the measured shear stress ratio L of the level 1 and level 2 ground motions, respectively.
Using the measured value of the liquefaction resistivity FL, the liquefaction index PL for the level 1 ground motion and the level 2 ground motion of the soft ground is respectively measured.
The liquefaction index PL for the level 1 earthquake motion is compared with the liquefaction occurrence condition liquefaction index PL _L determined based on past earthquake damage cases and importance of structures ,
When the value of the liquefaction index PL with respect to the level 1 earthquake motion larger becomes than the value of the liquefaction occurrence condition liquefaction index PL _L includes a liquefaction index PL with respect to the level 2 ground motion, the past earthquakes damage case and structures comparing the target liquefaction index PL _T which is determined on the basis of such importance,
When liquefaction index PL for the level 2 earthquake motion in the said soft ground is greater than the value of the target liquefaction index PL _T, using the formula and values of liquefaction resistance increase coefficient n of soil for calculating the liquefaction index PL , PL-q (change in the liquefaction index PL caused by the magnitude of the embankment load obtained by expressing the magnitude of the liquefaction index PL in the soft ground on the vertical axis and the magnitude of the embankment load q on the horizontal axis Curve): for calculating the target weight value of the load)
From the relationship diagram of the PL-q, target weight value of the load object corresponding to the target liquefaction index PL _T can be calculated,
It is characterized by
Or
Prior to the construction of the structure on the soft ground, a load object having a predetermined weight is placed on the soft ground for a predetermined time, and then the over-consolidation history effect generated by removing the load object is used, and the soft ground surface portion A non-soft ground layer having a predetermined thickness is formed, and a soft ground layer that becomes a liquefied layer is left in a lower layer of the non-soft ground layer, and the soft ground layer is used as a base isolation layer. And
Based on the N value that is the soil measurement value of the soft ground, a corrected Na value is obtained in consideration of the influence of the soil grain size in the soft ground, and the liquefaction resistance value R of the soft ground is calculated using the Na value. Measure and
Measure the shear stress ratio L at the time of earthquake of Level 1 ground motion and Level 2 ground motion in the soft ground,
Measure the liquefaction resistivity FL against level 1 and level 2 ground motions of the soft ground using the liquefaction resistance value R and the measured shear stress ratio L of the level 1 and level 2 ground motions, respectively.
Using the measured value of the liquefaction resistivity FL, the liquefaction index PL for the level 1 ground motion and the level 2 ground motion of the soft ground is respectively measured.
The liquefaction index PL for the level 1 earthquake motion is compared with the liquefaction occurrence condition liquefaction index PL _L determined based on past earthquake damage cases and the importance of the structure ,
When the value of the liquefaction index PL with respect to the level 1 earthquake motion larger becomes than the value of the liquefaction occurrence condition liquefaction index PL _L includes a liquefaction index PL with respect to the level 2 ground motion, the past earthquakes damage case and structures comparing the target liquefaction index PL _T which is determined on the basis of such importance,
When liquefaction index PL for the level 2 earthquake motion in the said soft ground is greater than the value of the target liquefaction index PL _T, using the formula and values of liquefaction resistance increase coefficient n of soil for calculating the liquefaction index PL , PL-q (change in the liquefaction index PL caused by the magnitude of the embankment load obtained by expressing the magnitude of the liquefaction index PL in the soft ground on the vertical axis and the magnitude of the embankment load q on the horizontal axis Create a relationship diagram of the curve representing: (for calculating the target weight value of the load)
From the relationship diagram of the PL-q, target weight value of the load object corresponding to the target liquefaction index PL _T is calculated,
And, the mounting time of the target weight value is calculated from the soil data obtained by measuring the soil of the soft ground,
It is characterized by
Or
The target liquefaction index PL _T was set to be updated by calculating the historical data,
It is characterized by
Or
The calculation of the target weight placement time can be calculated based on the amount of settlement of the soft ground,
It is characterized by this.

すなわち、本発明による免震地盤形成方法は、
軟弱地盤上にプレロードなどによるサーチャージ荷重を構造物建設に先立ち一定時間、一定の重量で与え、構造物建設時にはそれを取り除くだけで軟弱地盤を地表面から所定深さまでの期待しうる改良地盤（非軟弱地盤）に形成できる。 That is, the seismic isolation ground forming method according to the present invention is:
A surcharge load such as preload on a soft ground is given at a constant weight for a certain period of time prior to construction of the structure, and when the structure is constructed, the soft ground can be expected from the ground surface to a predetermined depth just by removing it. It can be formed on soft ground.

しかも前記改良地盤の形成と同時に大きな地震時などにおいて免震層として機能する軟弱地盤層を、前記改良地盤の下層において、最大の免震効果が得られるよう残置形成できるものである。 In addition, a soft ground layer that functions as a seismic isolation layer at the time of a large earthquake at the same time as the formation of the improved ground can be left in the lower layer of the improved ground so as to obtain the maximum seismic isolation effect.

地盤は、一度過圧密履歴を受けるといわゆる繰り返し抵抗が増加する。この増加程度は、過圧密比ＯＣＲのｎ乗に比例することが確認されている。 Once the ground receives an overconsolidation history, so-called repetitive resistance increases. It has been confirmed that the degree of increase is proportional to the nth power of the overconsolidation ratio OCR.

過圧密比ＯＣＲは、軟弱地盤上に盛土などを行い、それを除荷すると、除荷した地盤の地表面に近づくほど大きくなる。 The overconsolidation ratio OCR increases as the ground surface of the unloaded ground is approached when embankment or the like is performed on soft ground and then unloaded.

したがって、このような過圧密履歴を与えると地表面ほど液状化抵抗が増加することとなる。すなわち、改良された地盤が形成されるものとなる。 Therefore, when such an overconsolidation history is given, the liquefaction resistance increases toward the ground surface. That is, an improved ground is formed.

そして、このように改良された地盤の下層では軟弱地盤が残置され、地震時においてその残置された液状化層や粘性土地盤層に大きな非線形化による大きなひずみが生じ、これが地震外力を低減する機能を果たすものとなる。 And the soft ground is left in the lower layer of the ground improved in this way, and during the earthquake, the liquefied layer and the viscous ground layer that remain are subjected to large distortion due to large non-linearization, which reduces the seismic external force Will be fulfilled.

ところで、地表面近くの地層ほど繰り返し抵抗が増加しているので地盤下部よりも地表面は相対的に繰り返し抵抗が大きくなっていることは既に述べたとおりである。 By the way, as the stratum closer to the ground surface repeatedly increases in resistance, the ground surface has a relatively larger resistance repeatedly than the lower part of the ground as already described.

しかし、相対的に繰り返し抵抗が小さな層、すなわち非軟弱地盤に改良された地表面近くの地層よりさらに下層には残置された軟弱地盤層が存在しており、剛性が低下すると地震波はその層に集中することになる。 However, there is a layer with relatively low resistance, that is, a soft ground layer that remains in the layer below the ground surface that has been improved to a non-soft ground. To concentrate.

そして、さらに剛性が低下すると、その残置された軟弱地盤層で地震力は著しく低下し、もって前記軟弱地盤層が免震層としての機能、効果を発揮することになる。 When the rigidity is further lowered, the seismic force is remarkably lowered in the remaining soft ground layer, and the soft ground layer exhibits a function and an effect as a seismic isolation layer.

本発明によれば、軟弱地盤の地表面近くの地盤をいわゆる過圧密履歴作用を用いて自動的に改良地盤に形成できる。しかも、液状化など軟弱地盤の非線形化を利用した地盤の適切な免震層形成を軟弱地盤の内部に特に積極的に手を加えることなく前記の改良地盤の下層所定範囲に容易に形成できる。 According to the present invention, the ground near the ground surface of the soft ground can be automatically formed on the improved ground using the so-called overconsolidation history action. In addition, it is possible to easily form an appropriate seismic isolation layer for the ground using the non-linearization of the soft ground such as liquefaction in the predetermined range below the improved ground without actively changing the inside of the soft ground.

そして、このような形成方法によって、地表の住宅・工場・グラウンドなどの諸施設、埋設管・埋設タンク・半地下構造物の大きな地震に対する地震外力をむやみにあげることなく大きな免震効果を構築することが可能となる（図５，図６参照）。 And, by such a formation method, it builds a large seismic isolation effect without unnecessarily increasing the earthquake external force against large earthquakes of houses, factories, ground, etc., buried pipes, buried tanks, and semi-underground structures (See FIGS. 5 and 6).

特に、シルトなどの細粒な土からなる地盤はサンドコンパクションパイルなどの地盤改良効果が低いが、本発明では、特にこのような地盤で効果的に機能する。 In particular, the ground made of fine soil such as silt has a low ground improvement effect such as a sand compaction pile, but in the present invention, it functions particularly effectively on such ground.

以下、本発明を図に示す実施例に基づいて説明する。 Hereinafter, the present invention will be described based on embodiments shown in the drawings.

まず、軟弱地盤１上（図１参照）に荷重物２（図２参照）を載置する。この載置物２の種類に関しては何ら限定されない。すなわち、土砂でも構わないし、産業廃棄物でも構わないし、ゴミでも構わないし、鉄くずでも構わないし、アースアンカーなどによって加圧しても構わない。
しかして、本実施例では一般に多く存する残土を軟弱地盤１上に盛り土することにより荷重物２の載置と想定する。 First, the load 2 (see FIG. 2) is placed on the soft ground 1 (see FIG. 1). There is no limitation on the type of the object 2. That is, it may be earth and sand, industrial waste, garbage, iron scraps, or pressurization with an earth anchor or the like.
Therefore, in this embodiment, it is assumed that the load 2 is placed by depositing a large amount of remaining soil on the soft ground 1.

よって、将来、住宅地として開発したい地域につき、その前段階では残土置き場などとして活用し、所定時間経過後、軟弱地盤の地表面近くが改良地盤として有効に改良され、その下層には自動的に有効的な免震層を形成することが期待できる。 Therefore, the area that you want to develop as a residential area in the future will be used as a remaining soil storage place in the previous stage, and after a predetermined time, the ground surface of the soft ground will be effectively improved as improved ground, and the lower layer will be automatically It can be expected to form an effective seismic isolation layer.

ここで、残土などの荷重物２の載置は、例えば軟弱地盤１を改良したいとする領域にわたって盛り土されて行なわれる。そして、どの程度の載置時間で、どの程度の重量の盛り土を行うかは前記軟弱地盤１の土質により異なる。
よって、まず前記軟弱地盤１の土質を調査することが重要となる。 Here, placement of the load 2 such as the remaining soil is performed, for example, by embedding over an area where the soft ground 1 is desired to be improved. Then, how much embedding is performed in what amount of mounting time depends on the soil quality of the soft ground 1.
Therefore, it is important to investigate the soil quality of the soft ground 1 first.

その土質調査の重要性を示す例を挙げれば、前記土質測定などから軟弱地盤１の液状化抵抗Ｒ（動的せん断強度比）が求められ、その土質などの違いによりどの程度の載置時間で、どの程度の重量の盛り土とするのが最適なのかが決定できる。
（１）地盤の液状化抵抗Ｒ（動的せん断強度比）の測定
以下に液状化抵抗Ｒを測定する一例を示す。
当該軟弱地盤１において、標準貫入試験を行い当該地盤における土質のＮ値を求める。
例えば、地盤の液状化抵抗Ｒは、繰り返し三軸強度比RL、地震動特性による補正係数Cwの積で定義される。

従って前記Ｎ値を決定するために、先ず標準貫入試験（図４参照）を行う必要があるのである。
ここに、標準貫入試験とは、動的サウンディングの一種で、地盤のＮ値（標準貫入試験で測定する打撃回数）を求める試験をいう。図４から理解されるように、ボーリングなどにより削孔し、その中にサンプラーをロッド先端に接続し、後端にノッキングヘッドとガイド用ロッドを取り付け、重量63.5kgのハンマーを75cmの高さから自由落下させ、サンプラーが30cm貫入する打撃回数を求める。この打撃回数がＮ値となる。
しかして、測定された土質のＮ値により地盤の固さや締りの程度がわかる。
また、当該軟弱地盤１において、前記土を採取して液状化抵抗増加係数ｎや、細粒分含有率ＦＣ（％）、平均粒径Ｄ₅₀等をも求める。
尚、粒径は、標準貫入試験により得られる試料を粒度分析して求めた値でも構わない。
前記標準貫入試験から得られたＮ値を基に下記演算により、粒度の影響を考慮した補正Ｎ値＝Naが求められる。
（砂質土の場合） As an example showing the importance of the soil investigation, the liquefaction resistance R (dynamic shear strength ratio) of the soft ground 1 is obtained from the soil measurement and the like. It is possible to determine how much weight is optimal for embankment.
(1) Measurement of ground liquefaction resistance R (dynamic shear strength ratio) An example of measuring the liquefaction resistance R is shown below.
In the soft ground 1, a standard penetration test is performed to determine the N value of the soil in the ground.
For example, the liquefaction resistance R of the ground is defined by the product of the repeated triaxial strength ratio RL and the correction coefficient Cw based on the ground motion characteristics.

Therefore, in order to determine the N value, it is necessary to first perform a standard penetration test (see FIG. 4).
Here, the standard penetration test is a kind of dynamic sounding and refers to a test for determining the N value of the ground (the number of impacts measured in the standard penetration test). As can be seen from Fig. 4, drilling holes, etc., connecting a sampler to the tip of the rod, attaching a knocking head and guide rod to the rear end, and a 63.5kg weight hammer from a height of 75cm Let it fall freely and find the number of hits that the sampler can penetrate 30cm. The number of hits is an N value.
Therefore, the hardness of the ground and the degree of tightening can be understood from the measured N value of the soil.
Further, in the soft ground 1, the soil is collected and the liquefaction resistance increasing coefficient n, the fine particle content FC (%), the average particle diameter D _{50 and the} like are also obtained.
The particle diameter may be a value obtained by particle size analysis of a sample obtained by a standard penetration test.
Based on the N value obtained from the standard penetration test, a corrected N value = Na considering the influence of the particle size is obtained by the following calculation.
(For sandy soil)

（れき質土の場合）

(For rubble soil)

上記のNa値から、R_L及びＲが求められる。

From the Na value, R _L and R are obtained.

（２）地震時せん断応力比Ｌの測定
次に地震時せん断応力比Ｌについての一測定例を以下に示す。

(2) Measurement of the shear stress ratio L during an earthquake Next, an example of measuring the shear stress ratio L during an earthquake is shown below.

上記をまとめると

To summarize the above

従って地震時せん断応力比Ｌを求めるに際しては、地下水位面の深浅部における土の単位体積重量（ｋＮ／ｍ³）を明らかにしておく必要がある。

Therefore, when determining the shear stress ratio L during an earthquake, it is necessary to clarify the unit volume weight (kN / m ³ ) of the soil in the shallow part of the groundwater level.

従ってＲについても、各層毎に異なる値となると考えられる。

（３）液状化抵抗率ＦＬの測定
上記方法でＲ及びＬが定まることから、液状化に対する抵抗率ＦＬを算出し、この値が、1.0以下の土層については、液状化するものとみなされる。
ＦＬ＝Ｒ／Ｌ
：Ｒ；液状化抵抗（動的せん断強度比）、Ｌ；地震時せん断応力比
以上のことから、ＦＬの値は、一定の条件の合致することを前提とすれば、土質の定数等から、算出可能である。
また、各層毎に異なる値になる。

（４）液状化指数ＰＬの測定
地盤各土層のＦＬから、当該地盤の液状化指数ＰＬが求められる。

Therefore, it is considered that R also has a different value for each layer.

(3) Measurement of liquefaction resistivity FL Since R and L are determined by the above method, the resistivity FL against liquefaction is calculated, and soil layers having this value of 1.0 or less are considered to be liquefied. .
FL = R / L
: R: Liquefaction resistance (dynamic shear strength ratio), L: Since the earthquake shear stress ratio or higher, the FL value is based on soil constants, etc., assuming that certain conditions are met. It can be calculated.
Moreover, it becomes a different value for each layer.

(4) Measurement of liquefaction index PL The liquefaction index PL of the ground is obtained from the FL of each soil layer.

従ってＦＬが、定まればＰＬも定まる。
具体的には、各層毎のＲ、Ｌ、ＦＬを算出し、
当該層における（１−ＦＬ）（１０−０．５ｘ）ｄｘを計算する。次に0ｍ層から20m層までの各値を積算することにより定められる。

（５）当該軟弱地盤１の液状化指数ＰＬと液状化発生条件液状化指数ＰＬ_Ｌとの比較
当該ＰＬと液状化発生条件液状化指数ＰＬ_Ｌを比較し、当該ＰＬ値がＰＬ_Ｌ値より大きいことを確認する。
小さい場合には、免震層は、形成されないので別の免震対策が必要となる。
本発明は、過圧密履歴によって当該地盤のＲを大きくし、その結果当該地盤のＰＬ値を下げることをポイントとするものだからである。
当該軟弱地盤のＰＬ値が大きい場合以下の場合に進む。

（６）当該軟弱地盤のＰＬ−ｑ関係図を作成する
土質試験から得た、当該軟弱地盤１の液状化抵抗増加係数ｎから、ＰＬ−ｑ関係図が作成される。
すなわち過圧密比ＯＣＲと液状化抵抗Ｒの関係は、下記となる。

Therefore, if FL is determined, PL is also determined.
Specifically, R, L, FL for each layer is calculated,
Calculate (1-FL) (10-0.5x) dx in the layer. Next, it is determined by integrating each value from 0m layer to 20m layer.

(5) greater than the soft ground 1 compares the comparison the PL and liquefaction Condition liquefaction index PL _L between liquefaction index PL and liquefaction Condition liquefaction index PL _L, the PL value PL _L value Make sure.
If it is small, the seismic isolation layer is not formed, so another seismic isolation measure is required.
This is because the point of the present invention is to increase the R of the ground based on the overconsolidation history and, as a result, lower the PL value of the ground.
When the PL value of the soft ground is large, the process proceeds to the following case.

(6) A PL-q relationship diagram is created from the liquefaction resistance increase coefficient n of the soft ground 1 obtained from a soil test for creating a PL-q relationship diagram of the soft ground.
That is, the relationship between the overconsolidation ratio OCR and the liquefaction resistance R is as follows.

上記関係式から、図７に示されるＰＬ−ｑ関係図が作成されるのである。
このＰＬ―ｑ関係図から、目標液状化指数ＰＬ_Ｔに対応する目標載荷荷重ｑtが定められる。
例えばｑt＝3.4tf/m²の場合、盛土高さや密度などの仕様を定める。
1.7t/m³の密度の土を使用する場合には、盛土高さは、3.4/1.7=2.0より、2.0mとの値が定まる。
なお、盛り土の密度と高さによって、その荷重は変わる。従って、盛り土の密度と高さがわかれば、当該盛り土の荷重、すなわち重量がわかる。
次に、どの程度の時間、荷重物２を載置するかを決定する。かかる載置時間の決定は、例えば現場での前記軟弱地盤１の沈下幅によっても認識出来る。
軟弱地盤１上に荷重物２を載置した当初は図２に示す様に軟弱地盤１は、急激な沈下量Sを示す。

From the above relational expression, the PL-q relation diagram shown in FIG. 7 is created.
This PL-q relationship diagram, the target applied load qt corresponding to the target liquefaction index PL _T is determined.
For example, when qt = 3.4 tf / m ² , specifications such as embankment height and density are determined.
When soil with a density of 1.7 t / m ³ is used, the embankment height is determined to be 2.0 m from 3.4 / 1.7 = 2.0.
The load varies depending on the density and height of the embankment. Therefore, if the density and height of the bank are known, the load, that is, the weight of the bank can be determined.
Next, it is determined how long the load 2 is placed. The determination of the placement time can be recognized by, for example, the settlement width of the soft ground 1 at the site.
Initially, when the load 2 is placed on the soft ground 1, the soft ground 1 exhibits an abrupt settlement S as shown in FIG.

すなわち、軟弱地盤１上で荷重物２により荷重を増加させると、軟弱地盤１中において、土粒子間の間隙が小さくなる。そして、間隙が小さくなった分、間隙の水が時間の経過ともない排水される。さらに、時間の経過とともに前記間隙水の移動が止まり、これに伴い軟弱地盤１の沈下も安定する。 That is, when the load is increased by the load 2 on the soft ground 1, the gap between the soil particles is reduced in the soft ground 1. Then, as the gap becomes smaller, the water in the gap is drained over time. Furthermore, the movement of the pore water stops with the passage of time, and the subsidence of the soft ground 1 is stabilized accordingly.

この沈下が安定するまでの時間、すなわち沈下が起こっている時間中荷重物を載置しておく。そして、例えば、沈下測定器などの測定により、地盤の沈下が終了したとされたときに前記の載置物を除荷することになる。
この様に、一定期間の間、前記盛土などによる荷重物の載荷を放置し，その後前記の荷重物を除荷して元の状態に戻す。 The load is placed during the time until the settlement is stabilized, that is, during the time when the settlement is occurring. Then, for example, when the ground subsidence is finished by measurement with a subsidence measuring instrument or the like, the above-mentioned mounted object is unloaded.
In this way, the loading of the load by the embankment or the like is allowed to stand for a certain period, and then the load is unloaded and returned to the original state.

本発明はこのような荷重物の載荷工程、及び除荷工程で軟弱地盤に過圧密履歴を与え、地表面近くの軟弱地盤層を改良して非軟弱地盤層にし、かつその下層に軟弱地盤層を残置してそれを免震層とするのである（図３参照）。
次に、図８に示すフローチャートに基づき具体例を挙げて説明する。
まず、各種設計条件の想定、設定が行われる（ステップ１００）。
各種の設計条件を例えば以下のように設定される。 The present invention gives an overconsolidation history to the soft ground in the loading process and unloading process of such a load, improves the soft ground layer near the ground surface into a non-soft ground layer, and the soft ground layer below it Is left as a seismic isolation layer (see Fig. 3).
Next, a specific example will be described based on the flowchart shown in FIG.
First, various design conditions are assumed and set (step 100).
Various design conditions are set as follows, for example.

液状化発生条件液状化指数PL_L：5
また、地震外力をレベル１地震としk_ｈｇ=0.18として設定する。 Liquefaction occurrence condition Liquefaction index PL _L : 5
Also, set the earthquake external force as level 1 earthquake and _khg = 0.18.

改良後の目標液状化指数PL_Ｔ：15
ここで、液状化発生条件液状化指数PL_Ｌと改良後の目標液状化指数PL_Ｔの設定は，過去の地震被害事例や構造物の重要度などに基づき決めることが考えられる（図２０参照）。 Target liquefaction index PL _T after improvement: 15
Here, setting of the target liquefaction index PL _T after the modification and liquefaction Condition liquefaction index PL _L is considered be determined on the basis of such importance of the past earthquakes damage case and structures (see FIG. 20) .

例えば，近年生じた大型地震の液状化発生の調査結果、すなわち、レベル2地震動による液状化被害調査などに基づき以下のように設定される。 For example, it is set as follows based on the survey results of liquefaction occurrence of large earthquakes that occurred in recent years, that is, liquefaction damage surveys due to Level 2 ground motion.

図２０により，液状化発生条件液状化指数として，レベル1地震動により求めたPL値が5以上のものは液状化しやすい地盤と判断できることから，PL_Ｌ値は5と設定する。 The Figure 20, a liquefaction occurrence condition liquefaction index, PL value determined by the level 1 earthquake motion from it 5 or more of it can be judged that liquefaction easily ground, PL _L value is set to 5.

次に，同じく図２０により、目標液状化指数としては、レベル2地震動により求めたPL値が15以下のものは液状化しにくい地盤と判断できることから、PL_T値を15と設定するがごときである。
尚、この際に、地盤条件も想定、設定される。すなわち、以下の条件は地盤調査および土質試験により求められる。

しかして、これらの条件により過圧密を受ける前の液状化抵抗Ｒ₀が求められる（図１３参照）（ステップ１０２）。
当該液状化抵抗Ｒ₀の算出については既に説明したのでここでは省略する。
次に、液状化発生の確認として地盤のＰＬ値が求められる（ステップ１０４）。 Next, as shown in FIG. 20, as the target liquefaction index, a PL _T value of 15 or less obtained from level 2 ground motion can be determined as a ground that is difficult to liquefy, so the PLT value is set to 15. .
At this time, ground conditions are also assumed and set. That is, the following conditions are obtained by ground survey and soil test.

Accordingly, the liquefaction resistance R ₀ before the overconsolidation is obtained under these conditions (see FIG. 13) (step 102).
Since the calculation of the liquefaction resistance R ₀ has already been described, it is omitted here.
Next, as a confirmation of the occurrence of liquefaction, the PL value of the ground is obtained (step 104).

例えば地震外力k_ｈｇを0.18と小さくして地震時せん断応力比L（図１４参照）を求め計算を行い（図１６参照）、レベル１地震動に対する液状化指数PLが求められる。かかるＦＬ値の算出についても既に説明した。
ここで、ＰＬ値は１０．１として求められた。
その後、ＰＬ値とＰＬ_Ｌ値が比較され（ステップ１０６）、ＰＬ_Ｌ値がＰＬ値よりも大なるときには（ステップ１０６でＮＯ）、免震層が形成されない地盤と想定されるので別の免震対策を必要とすることになる（ステップ１０７）。 For example, the seismic external force k _hg is reduced to 0.18, the earthquake shear stress ratio L (see FIG. 14) is obtained and calculated (see FIG. 16), and the liquefaction index PL for level 1 ground motion is obtained. The calculation of the FL value has already been described.
Here, the PL value was determined as 10.1.
Thereafter, the PL value and PL _L value is compared (step 106), PL when _{the L} value is larger becomes than PL value (NO in step 106), another base-isolated because it is assumed Ground seismic isolation layer is not formed A countermeasure is required (step 107).

また、ＰＬ_Ｌ値がＰＬ値よりも小なるときには（ステップ１０６でＹＥＳ）、レベル２地震動に対する、地震時せん断応力比Ｌ（図１５参照）より求めた改良前液状化抵抗率ＦＬ（図１７参照）から算出されるＰＬ値とＰＬ_Ｔ値が比較され（ステップ１０８）、ＰＬ_Ｔ値がＰＬ値よりも大なるときには（ステップ１０８でＮＯ）、すでに目標の対策値に達しているので対策が不要と判断される（ステップ１０９）。 Further, when the PL _L value smaller becomes than PL value (YES at step 106), levels for 2 earthquake motion, before improvement liquefaction resistivity FL (see FIG. 17 determined from seismic shear stress ratio L (see FIG. 15) ) PL value and PL _T values calculated are compared from (step 108), NO at (step 108 when the PL _T value larger becomes than PL value), already required measures since reaching measures values of target Is determined (step 109).

しかし、ＰＬ_Ｔ値がＰＬ値よりも小なるときには（ステップ１０８でＹＥＳ）、地盤のｎ値などが求められ、地盤のＰＬ−Ｈ関係図が作製される（図１８参照）。なお、このＰＬ−Ｈ関係図はＰＬ−ｑ関係図（図７参照）から盛土密度を考慮しｑをＨに変更したものである（ステップ１１２）。
尚、ここでは、（10.1=PL）>（ PL_L=5 ）であるので，前提として液状化の発生する地盤と判断されることとなる。 However, when the PL _T value smaller becomes than PL value (YES at step 108), such as n value of the ground is determined, PL-H relationship diagram of the ground is produced (see FIG. 18). This PL-H relationship diagram is obtained by changing q to H in consideration of the embankment density from the PL-q relationship diagram (see FIG. 7) (step 112).
Here, since (10.1 = PL)> (PL _L = 5), it is determined that the ground is liquefied.

そして、当該関係図によりＰＬ_Ｔ値に対応する目標盛土高さＨが求められるのである（ステップ１１２）。 Then, it is the goal embankment height H corresponding to the PL _T value by the relationship diagram is determined (step 112).

例えば、PL_Ｔ：（改良後の目標PL ）=15より，PLが低くなるのは盛土高さ8ｍのときとされるなどである。
さらに、盛土高さ8ｍの時の液状化地盤の変化が求められ、どのように液状化層が残り、どのように非液状化層が形成されるかなど確認されることになる（図１９参照）。 For example, from PL _T : (target PL after improvement) = 15, the PL is lowered when the embankment height is 8 m.
Furthermore, the change in the liquefied ground at the height of the embankment is 8 m, and it will be confirmed how the liquefied layer remains and how the non-liquefied layer is formed (see FIG. 19). ).

しかして、前記Ｈの値により盛り土高さや土の密度など盛り土の仕様が決定され、その重量も確定される（ステップ１１４）。 Therefore, the specifications of the embankment such as the embankment height and the soil density are determined by the value of H, and the weight thereof is also determined (step 114).

そして、最終的に地盤の圧密特性などにより一次圧密終了などを目処に載荷時間が決定される（ステップ１１６）。
尚、液状化地盤は，一般的には砂質地盤であり、このような地盤は排水性が高いので、1ヶ月程度以上の載荷を行えば十分であると考えられる。
本発明が特に、有効に適用されるのはシルト質の地盤と考えられる。
このような場合、一次圧密時間の計測は予め実際の現場での土質の計測データや過去の土質計測データに基づき推定され、設定される。
例えば，室内試験で圧密係数c_vが求められている場合には，次式より盛土載荷時間が推定され、設定されるのである。 Finally, the loading time is determined with the aim of the completion of the primary consolidation or the like based on the consolidation characteristics of the ground (step 116).
It should be noted that the liquefied ground is generally sandy ground, and such ground is highly drainable, so it is considered sufficient to load it for about one month or more.
It is considered that the present invention is particularly effectively applied to silty ground.
In such a case, the measurement of the primary consolidation time is estimated and set in advance on the basis of actual soil measurement data and past soil measurement data.
For example, when the consolidation coefficient _cv is obtained in a laboratory test, the embankment loading time is estimated and set by the following equation.

次に、本発明による改良地盤及び免震地盤形成はコンピュータを使用して自動的にスムーズに行うことが出来る。
よって次に、コンピュータによる免震地盤自動形成システムにつき説明する（図９参照）。

Next, the improved ground and seismic isolation ground formation according to the present invention can be performed automatically and smoothly using a computer.
Therefore, next, an automatic seismic isolation ground forming system using a computer will be described (see FIG. 9).

符号１０は土質測定手段を示し、該土質測定手段１０は前記した改良すべき軟弱地盤１の土質を測定するものであり、例えば、前述の標準貫入試験などが該当する。
標準貫入試験においては、軟弱地盤のＮ値（標準貫入試験で測定する打撃回数）などが求められる。
そして、測定された土質のＮ値により地盤の固さや締りの程度がわかる。また、当該軟弱地盤１において、土質のサンプルを採取し、土質試験することにより液状化抵抗増加係数ｎや、細粒分含有率ＦＣ（％）、平均粒径Ｄ₅₀等をも求められる。 Reference numeral 10 denotes a soil measurement means, which measures the soil quality of the soft ground 1 to be improved, and corresponds to, for example, the standard penetration test described above.
In the standard penetration test, the N value of soft ground (number of impacts measured in the standard penetration test) and the like are required.
And the hardness of the ground and the degree of tightening can be understood from the measured N value of the soil. Further, in the soft ground 1, a sample of soil was taken, and increased liquefaction resistance factor n by soil testing, fine fraction content FC (%), also required an average particle diameter D ₅₀ and the like.

そして、これら求められた土質データ１２はサーバコンピュータ１１の記憶部１３に保存される。 Then, the obtained soil data 12 is stored in the storage unit 13 of the server computer 11.

また、この土質データ１２を用いて液状化抵抗値Ｒが液状化抵抗値測定手段１４により求められる。さらに、前記の土質データ１２を用いてレベル１地震動とレベル２地震動に対して地震せん断時応力比Ｌが地震せん断時応力比測定手段１５により測定される。 Further, the liquefaction resistance value R is obtained by the liquefaction resistance value measuring means 14 using the soil data 12. Furthermore, using the soil data 12, the earthquake shear stress ratio L is measured by the earthquake shear stress ratio measuring means 15 for the level 1 earthquake motion and the level 2 earthquake motion.

そして、上記の前記液状化抵抗値Ｒと地震時せん断応力比Ｌの測定値を用いて液状化抵抗率測定手段１６によってレベル１地震動とレベル２地震動に対して液状化抵抗率ＦＬが測定される。
さらに、前記液状化抵抗率ＦＬの測定値から液状化指数測定手段１７によってレベル１地震動とレベル２地震動に対して液状化指数ＰＬが測定される。
まず、レベル１地震動によって求められた液状化指数ＰＬ値と液状化発生条件液状化指数（ＰＬ_Ｌ）３０とが比較手段１８によって比較され、前記レベル１地震動によって求められた液状化指数ＰＬが液状化発生条件液状化指数ＰＬ_Ｌ値３０より大きいときは、その後、レベル２地震動によって求められた液状化指数ＰＬ値と目標液状化指数（ＰＬ_Ｔ）２２とが比較手段１８によって比較され、前記液状化指数ＰＬが目標液状化指数（ＰＬ_Ｔ）２２の値より大きいときには、作製手段１９により前記液状化指数ＰＬと前記液状化抵抗増加係数ｎとの値などを用いてＰＬ−ｑ（荷重物の目標重量値）の関係図が作製される。 The liquefaction resistivity FL is measured by the liquefaction resistivity measuring means 16 for the level 1 and level 2 earthquake motions using the measured values of the liquefaction resistance value R and the earthquake shear stress ratio L. .
Further, the liquefaction index PL is measured by the liquefaction index measuring means 17 from the measured value of the liquefaction resistivity FL for the level 1 earthquake and the level 2 earthquake.
First, the liquefaction index PL value obtained by the level 1 earthquake motion and the liquefaction occurrence condition liquefaction index (PL _L ) 30 are compared by the comparison means 18, and the liquefaction index PL obtained by the level 1 earthquake motion is liquid. When the liquefaction generation condition liquefaction index PL _L value is larger than 30, then the liquefaction index PL value obtained by the level 2 earthquake motion and the target liquefaction index (PL _T ) 22 are compared by the comparison means 18, and the liquid state When the liquefaction index PL is greater than the target liquefaction index (PL _T ) 22, the production means 19 uses the values of the liquefaction index PL and the liquefaction resistance increase coefficient n, etc. to obtain PL-q (load A relationship diagram of (target weight value) is created.

そして、重量算出手段２０によって前記ＰＬ−ｑ（荷重物の目標重量値）の関係図から目標液状化指数ＰＬ_Ｔに対応する荷重物の目標重量値が算出されることになる。 Then, so that the target weight value of the PL-q load object corresponding the relationship diagram (target weight value of the load thereof) to a target liquefaction index PL _T is calculated by the weight calculation unit 20.

さらに、前記の土質データ１２などを参考に載置時間算出手段２１では前記目標重量値の載置時間が算出されることになる。 Further, the placement time calculation means 21 calculates the placement time of the target weight value with reference to the soil data 12 and the like.

ところで、土質データ１２はサーバコンピュータ１１（図１０参照）の記憶部１３において保存されているが、該土質データ１２は各地域の軟弱地盤１における土質データ１２が収集されている。
また、載置時間の算出についても前記土質データ１２が用いられるが、その予め推定された載置時間と共に、実際の現場において軟弱地盤１の沈下量Sを測定し、一次沈下が終了したときに載置時間の終了とすることも出来る。 By the way, although the soil data 12 is preserve | saved in the memory | storage part 13 of the server computer 11 (refer FIG. 10), this soil data 12 has collected the soil data 12 in the soft ground 1 of each area.
In addition, the soil data 12 is used for the calculation of the placement time, and the subsidence amount S of the soft ground 1 is measured at the actual site together with the presumed placement time, and the primary settlement is completed. It is also possible to end the loading time.

ここで、土質測定手段１０，液状化抵抗値測定手段１４、地震せん断時応力比測定手段１５、液状化抵抗率測定手段１６、液状化指数測定手段１７，比較手段１８，作製手段１９、重量算出手段２０及び載置時間算出手段２１の動作はサーバコンピュータ１１でキーボードあるいはマウスなど入力部２３からの入力作業によりＣＰＵなどの制御部２４によって行われ、その内容はディスプレイなどの表示部２５で閲覧出来る。 Here, soil measurement means 10, liquefaction resistance measurement means 14, seismic shear stress ratio measurement means 15, liquefaction resistivity measurement means 16, liquefaction index measurement means 17, comparison means 18, preparation means 19, weight calculation The operations of the means 20 and the placement time calculating means 21 are performed by the control unit 24 such as a CPU by the input operation from the input unit 23 such as a keyboard or a mouse in the server computer 11, and the contents can be viewed on the display unit 25 such as a display. .

また、図１１から理解されるように、軟弱地盤１を改良し、免震層を形成する各現場で端末２６を用い、該端末２６につきインターネットなど通信回線網２７を介してサーバコンピュータ１１と接続し、実際の現場で行った土質の採取などからのデータを受信部２８，送信部２９によって送受信して、サーバコンピュータ１１側に送り、前記制御部２４で算出された荷重物２の載置重量あるいは載置時間をリアルタイムで取得することが出来るシステムとなっている。
Further, as understood from FIG. 11, the soft ground 1 is improved and a terminal 26 is used at each site where the seismic isolation layer is formed, and the terminal 26 is connected to the server computer 11 via a communication network 27 such as the Internet. Then, the weight of the load 2 calculated by the control unit 24 is transmitted and received by the receiving unit 28 and the transmitting unit 29 and transmitted to the server computer 11 side from the actual soil sampling and the like. Or it is a system which can acquire mounting time in real time.

本発明の概略構成を説明する概略構成説明図（その１）である。It is schematic structure explanatory drawing (the 1) explaining schematic structure of this invention. 本発明の概略構成を説明する概略構成説明図（その２）である。It is schematic structure explanatory drawing (the 2) explaining schematic structure of this invention. 本発明の概略構成を説明する概略構成説明図（その３）である。It is schematic structure explanatory drawing (the 3) explaining schematic structure of this invention. 標準貫入試験の概略を説明する概略構成説明図である。It is schematic structure explanatory drawing explaining the outline of a standard penetration test. 本発明の概略構成を説明する概略構成説明図（その４）である。It is schematic structure explanatory drawing (the 4) explaining schematic structure of this invention. 本発明の概略構成を説明する概略構成説明図（その５）である。It is schematic structure explanatory drawing (the 5) explaining schematic structure of this invention. 対策前の地盤のＰＬを示す曲線と、目標のＰＬを示す線とを交差させ、その箇所が必要な荷重を示すことを表したグラフである。It is the graph showing that the curve which shows PL of the ground before a countermeasure, and the line which shows target PL cross | intersect, and the location shows a required load. 本発明の構成を説明するフローチャートである。It is a flowchart explaining the structure of this invention. 本発明の構成を説明する概略構成説明図（その６）である。It is schematic structure explanatory drawing (the 6) explaining the structure of this invention. 本発明の構成を説明する概略構成説明図（その７）である。It is schematic structure explanatory drawing (the 7) explaining the structure of this invention. 本発明の構成を説明する概略構成説明図（その８）である。It is schematic structure explanatory drawing (the 8) explaining the structure of this invention. 本発明の概略構成を説明する概略構成説明図（その９）である。It is schematic structure explanatory drawing (the 9) explaining schematic structure of this invention. 本発明の概略構成を説明する概略構成説明図（その１０）である。It is schematic structure explanatory drawing (the 10) explaining schematic structure of this invention. 本発明の構成を説明する概略構成説明図（その１１）である。It is schematic structure explanatory drawing (the 11) explaining the structure of this invention. 本発明の概略構成を説明する概略構成説明図（その１２）である。It is schematic structure explanatory drawing (the 12) explaining schematic structure of this invention. 本発明の概略構成を説明する概略構成説明図（その１３）である。It is schematic structure explanatory drawing (the 13) explaining schematic structure of this invention. 本発明の概略構成を説明する概略構成説明図（その１４）である。It is schematic structure explanatory drawing (the 14) explaining schematic structure of this invention. 本発明の概略構成を説明する概略構成説明図（その１５）である。It is schematic structure explanatory drawing (the 15) explaining schematic structure of this invention. 本発明の概略構成を説明する概略構成説明図（その１６）である。It is schematic structure explanatory drawing (the 16) explaining schematic structure of this invention. 液状化発生条件液状化指数ＰＬ_Ｌの設定に使用される過去の液状化を分類した参考図である。Is a reference diagram classifying the past liquefaction is used to set the liquefaction Condition liquefaction index PL _L.

Explanation of symbols

１軟弱地盤
２荷重物
１０土質設定手段
１１サーバコンピュータ
１２土質データ
１３記憶部
１４液状化抵抗測定手段
１５地震せん断時応力比測定手段
１６液状化抵抗率測定手段
１７液状化指数測定手段
１８比較手段
１９作製手段
２０重量算出手段
２１載置時間算出手段
２２目標液状化指数
２３入力部
２４制御部
２５表示部
２６端末
２７通信回線網
２８受信部
２９送信部
３０液状化発生条件液状化指数 DESCRIPTION OF SYMBOLS 1 Soft ground 2 Loaded object 10 Soil setting means 11 Server computer 12 Soil data
13 Storage Unit 14 Liquefaction Resistance Measurement Unit 15 Seismic Shear Stress Ratio Measurement Unit 16 Liquefaction Resistivity Measurement Unit 17 Liquefaction Index Measurement Unit 18 Comparison Unit 19 Production Unit 20 Weight Calculation Unit 21 Mounting Time Calculation Unit 22 Target Liquefaction Index 23 Input unit 24 Control unit 25 Display unit 26 Terminal 27 Communication network 28 Reception unit 29 Transmission unit 30 Liquefaction occurrence condition Liquefaction index

Claims

Prior to the construction of the structure on the soft ground, a load object having a predetermined weight is placed on the soft ground for a predetermined time, and then the over-consolidation history effect generated by removing the load object is used, and the soft ground surface portion A non-soft ground layer having a predetermined thickness is formed, and a soft ground layer that becomes a liquefied layer is left in a lower layer of the non-soft ground layer, and the soft ground layer is used as a base isolation layer. And
Measure the liquefaction resistance value R of the soft ground using the N value which is the soil measurement value of the soft ground,
Measure the shear stress ratio L at the time of earthquake of level 2 ground motion in the soft ground,
Measure the liquefaction resistivity FL against level 2 ground motion of the soft ground using the measured value of the liquefaction resistance value R and the shear stress ratio L during earthquake of level 2 ground motion,
Using the measured value of the liquefaction resistivity FL for the level 2 earthquake motion, the liquefaction index PL for the level 2 earthquake motion of the soft ground is measured,
Compares the liquefaction index PL with respect to the level 2 ground motion, the target liquefaction index PL _T which is determined on the basis of such importance of the past earthquakes damage case and structures,
When liquefaction index PL for the level 2 earthquake motion in the said soft ground is greater than the value of the target liquefaction index PL _T, using the formula and values of liquefaction resistance increase coefficient n of soil for calculating the liquefaction index PL , PL-q (change in the liquefaction index PL caused by the magnitude of the embankment load obtained by expressing the magnitude of the liquefaction index PL in the soft ground on the vertical axis and the magnitude of the embankment load q on the horizontal axis Curve): for calculating the target weight value of the load)
From the relationship diagram of the PL-q, target weight value of the load object corresponding to the target liquefaction index PL _T can be calculated,
A seismic isolation ground formation method characterized by the above.

Prior to the construction of the structure on the soft ground, a load object having a predetermined weight is placed on the soft ground for a predetermined time, and then the over-consolidation history effect generated by removing the load object is used, and the soft ground surface portion A non-soft ground layer having a predetermined thickness is formed, and a soft ground layer that becomes a liquefied layer is left in a lower layer of the non-soft ground layer, and the soft ground layer is used as a base isolation layer. And
Measure the liquefaction resistance value R of the soft ground using the N value which is the soil measurement value of the soft ground,
Measure the shear stress ratio L at the time of earthquake of level 2 ground motion in the soft ground,
Measure the liquefaction resistivity FL against level 2 ground motion of the soft ground using the measured value of the liquefaction resistance value R and the shear stress ratio L during earthquake of level 2 ground motion,
Using the measured value of the liquefaction resistivity FL for the level 2 earthquake motion, the liquefaction index PL for the level 2 earthquake motion of the soft ground is measured,
Compares the liquefaction index PL with respect to the level 2 ground motion, the target liquefaction index PL _T which is determined on the basis of such importance of the past earthquakes damage case and structures,
When liquefaction index PL with respect to the level 2 earthquake motion is greater than the value of the target liquefaction index PL _T, using the formula and values of liquefaction resistance increase coefficient n of soil for calculating the liquefaction index PL, PL-q (A curve representing the change in the liquefaction index PL caused by the magnitude of the embankment load, obtained by expressing the magnitude of the liquefaction index PL on the vertical axis and the magnitude of the embankment load q on the horizontal axis: For the calculation of the target weight value)
From the relationship diagram of the PL-q, and calculates a target weight value of the load object corresponding to the target liquefaction index PL _T,
And calculating the placement time of the target weight value by soil data obtained by measuring the soil of the soft ground,
A seismic isolation ground formation method characterized by the above.

Prior to the construction of the structure on the soft ground, a load object having a predetermined weight is placed on the soft ground for a predetermined time, and then the over-consolidation history effect generated by removing the load object is used, and the soft ground surface portion A non-soft ground layer having a predetermined thickness is formed, and a soft ground layer that becomes a liquefied layer is left in a lower layer of the non-soft ground layer, and the soft ground layer is used as a base isolation layer. And
Based on the N value which is the soil measurement value of the soft ground, a corrected Na value is calculated in consideration of the influence of soil grain size in the soft ground, and the liquefaction resistance value R of the soft ground is measured using the Na value. And
Measure the shear stress ratio L at the time of earthquake of level 2 ground motion in the soft ground,
Measure the liquefaction resistivity FL against level 2 ground motion of the soft ground using the measured value of the liquefaction resistance value R and the shear stress ratio L during earthquake of level 2 ground motion,
Using the measured value of the liquefaction resistivity FL for the level 2 earthquake motion, the liquefaction index PL for the level 2 earthquake motion of the soft ground is measured,
Compares the liquefaction index PL with respect to the level 2 ground motion, the target liquefaction index PL _T which is determined on the basis of such importance of the past earthquakes damage case and structures,
When liquefaction index PL for the level 2 earthquake motion in the said soft ground is greater than the value of the target liquefaction index PL _T, using the formula and values of liquefaction resistance increase coefficient n of soil for calculating the liquefaction index PL , PL-q (change in the liquefaction index PL caused by the magnitude of the embankment load obtained by expressing the magnitude of the liquefaction index PL in the soft ground on the vertical axis and the magnitude of the embankment load q on the horizontal axis Curve): for calculating the target weight value of the load)
From the relationship diagram of the PL-q, target weight value of the load object corresponding to the target liquefaction index PL _T can be calculated,
A seismic isolation ground formation method characterized by the above.

Prior to the construction of the structure on the soft ground, a load object having a predetermined weight is placed on the soft ground for a predetermined time, and then the over-consolidation history effect generated by removing the load object is used, and the soft ground surface portion A non-soft ground layer having a predetermined thickness is formed, and a soft ground layer that becomes a liquefied layer is left in a lower layer of the non-soft ground layer, and the soft ground layer is used as a base isolation layer. And
Based on the N value which is the soil measurement value of the soft ground, a corrected Na value is calculated in consideration of the influence of soil grain size in the soft ground, and the liquefaction resistance value R of the soft ground is measured using the Na value. And
Measure the shear stress ratio L at the time of earthquake of level 2 ground motion in the soft ground,
Measure the liquefaction resistivity FL against level 2 ground motion of the soft ground using the measured value of the liquefaction resistance value R and the shear stress ratio L during earthquake of level 2 ground motion,
Using the measured value of the liquefaction resistivity FL for the level 2 earthquake motion, the liquefaction index PL for the level 2 earthquake motion of the soft ground is measured,
Compares the liquefaction index PL with respect to the level 2 ground motion, the target liquefaction index PL _T which is determined on the basis of such importance of the past earthquakes damage case and structures,
When liquefaction index PL with respect to the level 2 earthquake motion is greater than the value of the target liquefaction index PL _T, using the formula and values of liquefaction resistance increase coefficient n of soil for calculating the liquefaction index PL, PL-q (A curve representing the change in the liquefaction index PL caused by the magnitude of the embankment load, obtained by expressing the magnitude of the liquefaction index PL on the vertical axis and the magnitude of the embankment load q on the horizontal axis: For the calculation of the target weight value)
From the relationship diagram of the PL-q, and calculates a target weight value of the load object corresponding to the target liquefaction index PL _T,
And calculating the placement time of the target weight value by soil data obtained by measuring the soil of the soft ground,
A seismic isolation ground formation method characterized by the above.

Prior to the construction of the structure on the soft ground, a load object having a predetermined weight is placed on the soft ground for a predetermined time, and then the over-consolidation history effect generated by removing the load object is used, and the soft ground surface portion A non-soft ground layer having a predetermined thickness is formed, and a soft ground layer that becomes a liquefied layer is left in a lower layer of the non-soft ground layer, and the soft ground layer is used as a base isolation layer. And
Measure the liquefaction resistance value R of the soft ground using the N value which is the soil measurement value of the soft ground,
Measure the shear stress ratio L at the time of earthquake of Level 1 ground motion and Level 2 ground motion in the soft ground,
Measure the liquefaction resistivity FL against level 1 and level 2 ground motions of the soft ground using the liquefaction resistance value R and the measured shear stress ratio L of the level 1 and level 2 ground motions, respectively.
Using the measured value of the liquefaction resistivity FL, the liquefaction index PL for the level 1 ground motion and the level 2 ground motion of the soft ground is respectively measured.
The liquefaction index PL for the level 1 earthquake motion is compared with the liquefaction occurrence condition liquefaction index PL _L determined based on past earthquake damage cases and importance of structures ,
When the value of the liquefaction index PL with respect to the level 1 earthquake motion larger becomes than the value of the liquefaction occurrence condition liquefaction index PL _L includes a liquefaction index PL with respect to the level 2 ground motion, the past earthquakes damage case and structures comparing the target liquefaction index PL _T which is determined on the basis of such importance,
When liquefaction index PL for the level 2 earthquake motion in the said soft ground is greater than the value of the target liquefaction index PL _T, using the formula and values of liquefaction resistance increase coefficient n of soil for calculating the liquefaction index PL , PL-q (change in the liquefaction index PL caused by the magnitude of the embankment load obtained by expressing the magnitude of the liquefaction index PL in the soft ground on the vertical axis and the magnitude of the embankment load q on the horizontal axis Curve): for calculating the target weight value of the load)
From the relationship diagram of the PL-q, target weight value of the load object corresponding to the target liquefaction index PL _T can be calculated,
A seismic isolation ground formation method characterized by the above.

Prior to the construction of the structure on the soft ground, a load object having a predetermined weight is placed on the soft ground for a predetermined time, and then the over-consolidation history effect generated by removing the load object is used, and the soft ground surface portion A non-soft ground layer having a predetermined thickness is formed, and a soft ground layer that becomes a liquefied layer is left in a lower layer of the non-soft ground layer, and the soft ground layer is used as a base isolation layer. And
Measure the liquefaction resistance value R of the soft ground using the N value which is the soil measurement value of the soft ground,
Measure the shear stress ratio L at the time of earthquake of Level 1 ground motion and Level 2 ground motion in the soft ground,
Measure the liquefaction resistivity FL against level 1 and level 2 ground motions of the soft ground using the liquefaction resistance value R and the measured shear stress ratio L of the level 1 and level 2 ground motions, respectively.
Using the measured value of the liquefaction resistivity FL, the liquefaction index PL for the level 1 ground motion and the level 2 ground motion of the soft ground is respectively measured.
The liquefaction index PL for the level 1 earthquake motion is compared with the liquefaction occurrence condition liquefaction index PL _L determined based on past earthquake damage cases and importance of structures ,
When the value of the liquefaction index PL with respect to the level 1 earthquake motion larger becomes than the value of the liquefaction occurrence condition liquefaction index PL _L includes a liquefaction index PL with respect to the level 2 ground motion, the past earthquakes damage case and structures comparing the target liquefaction index PL _T which is determined on the basis of such importance,
When liquefaction index PL for the level 2 earthquake motion in the said soft ground is greater than the value of the target liquefaction index PL _T, using the formula and values of liquefaction resistance increase coefficient n of soil for calculating the liquefaction index PL , PL-q (change in the liquefaction index PL caused by the magnitude of the embankment load obtained by expressing the magnitude of the liquefaction index PL in the soft ground on the vertical axis and the magnitude of the embankment load q on the horizontal axis Curve): for calculating the target weight value of the load)
From the relationship diagram of the PL-q, target weight value of the load object corresponding to the target liquefaction index PL _T is calculated,
And calculating the placement time of the target weight value by soil data obtained by measuring the soil of the soft ground,
A seismic isolation ground formation method characterized by the above.

Prior to the construction of the structure on the soft ground, a load object having a predetermined weight is placed on the soft ground for a predetermined time, and then the over-consolidation history effect generated by removing the load object is used, and the soft ground surface portion A non-soft ground layer having a predetermined thickness is formed, and a soft ground layer that becomes a liquefied layer is left in a lower layer of the non-soft ground layer, and the soft ground layer is used as a base isolation layer. And
Based on the N value that is the soil measurement value of the soft ground, a corrected Na value is obtained in consideration of the influence of the soil grain size in the soft ground, and the liquefaction resistance value R of the soft ground is calculated using the Na value. Measure and
Measure the shear stress ratio L at the time of earthquake of Level 1 ground motion and Level 2 ground motion in the soft ground,
Measure the liquefaction resistivity FL against level 1 and level 2 ground motions of the soft ground using the liquefaction resistance value R and the measured shear stress ratio L of the level 1 and level 2 ground motions, respectively.
Using the measured value of the liquefaction resistivity FL, the liquefaction index PL for the level 1 ground motion and the level 2 ground motion of the soft ground is respectively measured.
The liquefaction index PL for the level 1 earthquake motion is compared with the liquefaction occurrence condition liquefaction index PL _L determined based on past earthquake damage cases and importance of structures ,
When the value of the liquefaction index PL with respect to the level 1 earthquake motion larger becomes than the value of the liquefaction occurrence condition liquefaction index PL _L includes a liquefaction index PL with respect to the level 2 ground motion, the past earthquakes damage case and structures comparing the target liquefaction index PL _T which is determined on the basis of such importance,
When liquefaction index PL for the level 2 earthquake motion in the said soft ground is greater than the value of the target liquefaction index PL _T, using the formula and values of liquefaction resistance increase coefficient n of soil for calculating the liquefaction index PL , PL-q (change in the liquefaction index PL caused by the magnitude of the embankment load obtained by expressing the magnitude of the liquefaction index PL in the soft ground on the vertical axis and the magnitude of the embankment load q on the horizontal axis Curve): for calculating the target weight value of the load)
From the relationship diagram of the PL-q, target weight value of the load object corresponding to the target liquefaction index PL _T can be calculated,
A seismic isolation ground formation method characterized by the above.

Prior to the construction of the structure on the soft ground, a load object having a predetermined weight is placed on the soft ground for a predetermined time, and then the over-consolidation history effect generated by removing the load object is used, and the soft ground surface portion A non-soft ground layer having a predetermined thickness is formed, and a soft ground layer that becomes a liquefied layer is left in a lower layer of the non-soft ground layer, and the soft ground layer is used as a base isolation layer. And
Based on the N value that is the soil measurement value of the soft ground, a corrected Na value is obtained in consideration of the influence of the soil grain size in the soft ground, and the liquefaction resistance value R of the soft ground is calculated using the Na value. Measure and
Measure the shear stress ratio L at the time of earthquake of Level 1 ground motion and Level 2 ground motion in the soft ground,
Measure the liquefaction resistivity FL against level 1 and level 2 ground motions of the soft ground using the liquefaction resistance value R and the measured shear stress ratio L of the level 1 and level 2 ground motions, respectively.
Using the measured value of the liquefaction resistivity FL, the liquefaction index PL for the level 1 ground motion and the level 2 ground motion of the soft ground is respectively measured.
The liquefaction index PL for the level 1 earthquake motion is compared with the liquefaction occurrence condition liquefaction index PL _L determined based on past earthquake damage cases and importance of structures ,
When the value of the liquefaction index PL with respect to the level 1 earthquake motion larger becomes than the value of the liquefaction occurrence condition liquefaction index PL _L includes a liquefaction index PL with respect to the level 2 ground motion, the past earthquakes damage case and structures comparing the target liquefaction index PL _T which is determined on the basis of such importance,
When liquefaction index PL for the level 2 earthquake motion in the said soft ground is greater than the value of the target liquefaction index PL _T, using the formula and values of liquefaction resistance increase coefficient n of soil for calculating the liquefaction index PL , PL-q (change in the liquefaction index PL caused by the magnitude of the embankment load obtained by expressing the magnitude of the liquefaction index PL in the soft ground on the vertical axis and the magnitude of the embankment load q on the horizontal axis Curve): for calculating the target weight value of the load)
From the relationship diagram of the PL-q, target weight value of the load object corresponding to the target liquefaction index PL _T is calculated,
And calculating the placement time of the target weight value by soil data obtained by measuring the soil of the soft ground,
A seismic isolation ground formation method characterized by the above.

The target liquefaction index PL _T was set to be updated by calculating the historical data,
The seismic isolation ground forming method according to claim 1, claim 2, claim 3, claim 4, claim 5, claim 6, claim 7, or claim 8.

The calculation of the target weight placement time can be calculated based on the amount of settlement of the soft ground,
The seismic isolation ground forming method according to claim 2, claim 4, claim 6 or claim 8.